Vaillant Combi Compact 242EB Fault codes & diagnostics

164 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural Gas 24 kW 1994-2001 Discontinued

Replaced by: Turbomax

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Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 81 High 21 Medium 61 Low

All 164 documented codes

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CONNECTION

Your boiler's main control panel has lost communication with its internal electronic brain, meaning the system cannot receive or process any instructions to work.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring Harness
  • Display Interface

Related codes

D,11

Your boiler is struggling to push hot water through your radiators because an external pump is not responding correctly.

High Engineer only £180-350

Parts commonly replaced

  • External circulation pump
  • Wiring harness
  • Control PCB

Related codes

D.0

Your boiler is struggling to reach its full heating power because the maximum heat output setting is incorrectly configured or restricted.

Medium Engineer only £80-£140

Parts commonly replaced

  • Main PCB
  • Gas Valve

Related codes

D.1

Your boiler is currently cooling itself down after providing heating by keeping the pump running temporarily.

Low DIY-safe

What to check first

  1. Wait for several minutes as this is a normal part of the boiler's operation
  2. Ensure your radiator valves are open to help the heat dissipate
  3. Check that your room thermostat is set to the desired temperature

Related codes

D.2

Your boiler is taking a short, temporary break to prevent the burner from turning on and off too frequently after reaching its target temperature.

Low DIY-safe

What to check first

  1. Wait for 5 to 15 minutes for the anti-cycling timer to finish naturally
  2. Check that your room thermostat is turned up high enough to call for heat
  3. Ensure all radiator valves (TRVs) are open to allow heat to dissipate

Related codes

D.3

Your boiler is currently showing you the temperature of the hot water as it flows through the system rather than a fault code.

Low DIY-safe

What to check first

  1. No action is required as this is a status message, not a fault.
  2. Wait for the hot water tap to be turned off for the display to return to the heating temperature.
  3. If the code persists when no water is running, check for a leaking or dripping tap.

Related codes

D.4

Your boiler is currently reading the live temperature from the warm start sensor, which is a normal status message rather than an actual fault code.

Low DIY-safe £0-80

What to check first

  1. Check if the comfort or 'warm start' mode is intentionally switched on
  2. Press the reset button if the boiler appears stuck on this display
  3. Monitor to see if the display changes to a standard temperature reading after a few minutes

Parts commonly replaced

  • NTC Temperature Sensor
  • Warm Start Sensor

Related codes

D.5

Your boiler is currently showing you what temperature it is aiming to reach rather than a specific error or mechanical failure.

Low DIY-safe

What to check first

  1. Check that your external room thermostat or smart controls are turned up to call for heat
  2. Observe if the display changes to a live temperature reading after a few moments
  3. Wait for the boiler to complete its current heating cycle as this is often an information code rather than a lockout

Related codes

D.7

Your boiler is displaying an information code rather than a fault, showing the temperature set for the pre-heated hot water function.

Low DIY-safe

What to check first

  1. Locate the right-hand control knob on the boiler fascia
  2. Turn the knob clockwise to enable or increase the warm start temperature
  3. Turn the knob fully anti-clockwise until it clicks to disable the warm start feature if not required

Related codes

D.8

Your boiler is currently receiving a signal from your thermostat or external programmer to provide heating.

Low DIY-safe

What to check first

  1. Check if your room thermostat is set higher than the current room temperature
  2. Verify if your central heating timer or smart app is currently set to an 'On' period
  3. Turn down the thermostat to see if the status code changes, confirming the controls are working

Related codes

Showing 11–20 of 164
D.9

Your boiler is receiving a specific temperature instruction from an external control or smart thermostat rather than using its own internal settings.

Low DIY-safe £0-120

What to check first

  1. Check your external thermostat or smart home app to see if it is set to a specific temperature
  2. Ensure the external controls are powered on and have fresh batteries
  3. Wait to see if the status changes as the external controller reaches its set point

Parts commonly replaced

  • External Thermostat
  • Analogue Control Module
  • Wiring Loom

Related codes

D.10

Your boiler's internal pump which circulates water to your radiators and taps has stopped working, meaning you likely have no heating or hot water.

High Engineer only £220-380

Parts commonly replaced

  • Internal circulation pump
  • Pump capacitor
  • PCB (Printed Circuit Board)

Related codes

D.12

Your boiler is having trouble communicating with the pump that provides and stores your hot water.

Medium Engineer only £150-350

Parts commonly replaced

  • Cylinder charging pump
  • Accessory module (VR40)
  • Wiring harness

Related codes

D.13

Your boiler is having trouble circulating hot water because of a potential issue with the internal pump or its electrical connection.

High Engineer only £180-350

Parts commonly replaced

  • Hot water circulation pump
  • Pump cable/wiring harness
  • Main PCB

Related codes

D.14

Your boiler is struggling to automatically adjust the water pump speed needed to circulate heat around your home.

Medium Engineer only £180-350

Parts commonly replaced

  • Modulating Pump
  • Main PCB
  • Pump PWM Cable

Related codes

D.15

Your boiler's internal pump is running at an incorrect speed, which prevents the system from moving heat to your taps or radiators effectively.

High Engineer only £180-350

Parts commonly replaced

  • Circulation Pump
  • Printed Circuit Board (PCB)

Related codes

D.17

Your boiler has detected that the water returning from your radiators is too hot, causing the system to automatically reduce its power output to protect itself.

Low DIY-safe £0-120

What to check first

  1. Ensure all radiator valves (TRVs) are fully open
  2. Check that there are no obstructions around the boiler vents
  3. Monitor if the boiler resumes normal operation after cooling down

Parts commonly replaced

  • None (Status code)
  • Return NTC thermistor
  • Bypass valve

Related codes

D.18

Your boiler is staying in a cooling-down phase where the pump runs continuously to prevent the internal components from overheating.

Low DIY-safe £0-120

What to check first

  1. Check if all radiator valves (TRVs) are fully open to allow water to circulate
  2. Ensure the room thermostat is turned down to see if the pump stops after several minutes
  3. Wait up to 20 minutes for the boiler to complete its natural overrun cycle

Parts commonly replaced

  • External Bypass Valve
  • Circulating Pump

Related codes

D.19

Your boiler is checking how the pump is running to move water around the system, which may cause temporary issues with heating performance.

Low Engineer only £120-250

Parts commonly replaced

  • Circulation Pump
  • PCB

Related codes

D.20

Your boiler is notifying you that it has reached the maximum temperature limit set for heating your hot water cylinder.

Low DIY-safe £0-80

What to check first

  1. Check the hot water temperature dial on the boiler control panel
  2. Turn the dial down slightly if it is set to maximum
  3. Monitor the display to see if the status code changes as the water cools

Parts commonly replaced

  • No parts usually required
  • NTC Temperature Sensor

Related codes

Showing 21–30 of 164
D.22

Your boiler is simply indicating that it is currently processing a request for hot water.

Low DIY-safe

What to check first

  1. Check that your hot water taps are fully closed
  2. Monitor the display to see if the code changes once the tap is turned off
  3. Ensure there are no dripping taps or leaks in your hot water pipework
D.23

Your boiler is currently set to summer mode, which means it will provide hot water but has temporarily disabled the central heating.

Low DIY-safe

What to check first

  1. Locate the main control knob for heating (usually marked with a radiator symbol).
  2. Turn the knob clockwise to your desired temperature setting to exit summer mode.
  3. Check that your external room thermostat or programmer is also calling for heat.

Related codes

D.24

Your boiler's internal water pressure is too low for it to operate safely, causing it to shut down temporarily.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop valves underneath the boiler.
  2. Slowly open both valves until you hear water entering the system.
  3. Close both valves tightly once the pressure gauge reaches 1.5 bar.

Parts commonly replaced

  • None (usually just requires topping up)
  • Filling loop valve
  • Expansion vessel

Related codes

D.25

Your boiler is simply indicating that it has received a signal from an external smart thermostat or control unit to start providing hot water.

Low DIY-safe

What to check first

  1. Check your hot water tap is turned off
  2. Ensure your external thermostat or controller settings are correct
  3. No action is required if hot water is currently being used

Related codes

D.26

Your boiler is having trouble communicating with an internal component or external accessory that helps manage its secondary electrical functions.

Medium Engineer only £120-280

Parts commonly replaced

  • Additional relay module
  • Wiring harness
  • Main PCB

Related codes

D.27

Your boiler's internal control system is struggling to communicate with an external accessory or control relay, which may affect how your heating or hot water turns on.

Medium Engineer only £120-280

Parts commonly replaced

  • Accessory relay module
  • Printed Circuit Board (PCB)
  • External wiring loom

Related codes

D.28

Your boiler's internal control board is having trouble communicating with an optional plugin component, usually related to external heating controls.

Medium DIY-safe £100-280

What to check first

  1. Turn off the power to the boiler at the fused spur switch
  2. Wait for 30 seconds
  3. Turn the power back on and check if the code clears
  4. Ensure your external thermostat or programmer is powered and has fresh batteries

Parts commonly replaced

  • Main PCB (Control Board)
  • Relay Module
  • External controls/wiring

Related codes

D.30

Your boiler is failing to light because the main control board is not sending the necessary signal to open the gas supply valves.

High Engineer only £180-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Gas Valve Wiring Harness

Related codes

D.33

Your boiler's fan is struggling to reach the correct speed required to safely push exhaust fumes out of the flue.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Fan motor
  • PCB
  • Air pressure switch

Related codes

D.34

Your boiler has stopped working because the fan is unable to reach the correct speed for the gas to safely ignite.

High Engineer only £250-450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Harness wiring

Related codes

Showing 31–40 of 164
D.35

Your boiler is currently set to provide warm water only and is not attempting to heat your radiators.

Medium DIY-safe

What to check first

  1. Locate the heating control knob on the front panel of the boiler.
  2. Turn the dial clockwise to a higher setting to re-enable the central heating mode.
  3. Check that your room thermostat is turned up to call for heat.

Related codes

D.36

Your boiler is struggling to detect when you turn on a hot tap, meaning your water might stay cold or fluctuate in temperature.

Medium Engineer only £120-210

Parts commonly replaced

  • Hot water flow sensor
  • Turbine sensor
  • Flow regulator

Related codes

D.40

Your boiler is displaying the current temperature it is aiming to reach for your heating or hot water, rather than a system fault.

Low DIY-safe

What to check first

  1. Check if the heating or hot water is running normally
  2. Press the 'i' button to exit the information display
  3. Monitor the boiler to see if it moves past the information code to show a temperature

Related codes

D.41

Your boiler is displaying the current temperature of the water returning from your radiators rather than indicating a specific fault.

Low DIY-safe

What to check first

  1. Check if the heating or hot water is still working as normal
  2. Press the 'i' button to exit the diagnostic menu if it was pressed by accident
  3. Monitor the boiler to see if the code changes to an 'F' (Fault) code

Related codes

D.44

Your boiler is having trouble detecting whether the flame is burning correctly, which is preventing it from staying on for safety.

High Engineer only £120-280

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Printed Circuit Board (PCB)

Related codes

D.47

Your boiler is having trouble communicating with the outdoor sensor that helps it adjust to the weather, meaning your heating might not be as efficient as usual.

Low DIY-safe £90-180

What to check first

  1. Locate the outdoor sensor on your external wall
  2. Check for any visible damage to the sensor unit or loose wires
  3. Gently wipe away any heavy dirt or debris covering the sensor

Parts commonly replaced

  • Outdoor temperature sensor
  • External wiring

Related codes

D.50

Your boiler's fan is struggling to run at the correct low speed required for efficient operation.

Medium Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)

Related codes

D.51

Your boiler's computer is reporting an internal memory error related to how it controls its fan speed.

High Engineer only £220-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • EEPROM chip

Related codes

D.58

Your boiler is currently receiving pre-heated water from your solar heating system and does not need to use gas to heat it further.

Low DIY-safe

What to check first

  1. No action required; this is an information code indicating the solar system is working correctly
  2. Monitor the display to ensure it returns to normal operation when solar heat is unavailable

Related codes

D.60

Your boiler has shut down because it has detected an unsafe build-up of heat too many times in a row, likely due to a circulation problem.

High DIY-safe £120-350

What to check first

  1. Check that your radiator valves are fully open to allow water to flow.
  2. Ensure your system water pressure is between 1.0 and 1.5 bar on the pressure gauge.
  3. Try resetting the boiler using the flame symbol or power button to clear the lock-out.

Parts commonly replaced

  • Circulation pump
  • Overheat thermostat
  • Main heat exchanger (cleaning or replacement)

Related codes

Showing 41–50 of 164
D.61

Your boiler has failed to ignite or stay lit too many times and has now locked itself out for safety reasons.

High Engineer only £120-350

Parts commonly replaced

  • Ignition Lead
  • Electrode Assembly
  • Gas Valve
  • PCB

Related codes

D.64

Your boiler is taking longer than expected to start up its flame, which suggests an early warning sign of a component starting to fail.

Low Engineer only £90-250

Parts commonly replaced

  • Ignition Electrodes
  • Lead Set
  • Gas Valve
  • PCB

Related codes

D.65

Your boiler is struggling to light its flame properly and has timed out for safety after several failed attempts.

High DIY-safe £100-£350

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. Check if other gas appliances in your home, like a hob, are working correctly
  3. Turn the boiler off and on again (reset) to see if the fault clears

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

D.67

Your boiler is temporarily resting to prevent the burner from turning on and off too frequently, which helps protect the internal components and improve efficiency.

Low DIY-safe

What to check first

  1. Wait for 5 to 15 minutes for the countdown to finish
  2. Ensure your room thermostat is turned up to call for heat
  3. Check that at least one radiator valve is fully open to allow water flow

Related codes

D.68

Your boiler is struggling to light its flame on the first try, which means it may eventually fail to provide heating and hot water.

Medium DIY-safe £100-280

What to check first

  1. Check that your gas stopcock is fully open and other gas appliances are working.
  2. Ensure your credit is topped up if you have a prepay gas meter.
  3. Restart the boiler using the reset button to see if it clears the temporary ignition error.

Parts commonly replaced

  • Ignition electrodes
  • Gas valve
  • Spark generator

Related codes

D.69

Your boiler has failed to light the flame twice in a row, meaning it cannot provide heating or hot water until the issue is resolved.

High DIY-safe £120-350

What to check first

  1. Check if other gas appliances, like a cooker, are working to ensure gas is reaching your home.
  2. If you have a prepayment meter, check that you have sufficient credit.
  3. Press the 'Reset' button (often marked with a flame symbol) on the boiler control panel.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

D.70

Your boiler is currently stuck in a diagnostic test mode used to check the internal valve that directs hot water to either your taps or your radiators.

Low DIY-safe £0-90

What to check first

  1. Turn the boiler off at the main power switch
  2. Wait for 30 seconds
  3. Turn the power back on to reset the diagnostic menus

Parts commonly replaced

  • None (Software reset)
  • Diverter Valve Motor

Related codes

D.71

Your boiler's heating temperature dial is set to its maximum power level, which is more of a status notification than a dangerous fault.

Low DIY-safe

What to check first

  1. Locate the radiator temperature control knob on the front of the boiler
  2. Turn the knob slightly counter-clockwise away from the maximum setting
  3. Check if the display changes to show a different numerical value

Related codes

D.72

Your boiler is briefly running its internal pump after heating your water to help cool the components down and prevent overheating.

Low DIY-safe
D.73

Your boiler is experiencing a slight calibration issue with its quick-start hot water feature, meaning it might take a moment longer to heat up than usual.

Low Engineer only £0-120

Parts commonly replaced

  • None (usually a settings adjustment)
  • Main PCB (if fault persists)

Related codes

Showing 51–60 of 164
D.75

Your boiler is taking too long to heat up your hot water cylinder, causing it to stop the process for safety.

Medium DIY-safe £100-280

What to check first

  1. Check that the isolation valves on the pipework leading to your hot water cylinder are fully open.
  2. Ensure your cylinder thermostat is not set to an unusually high temperature.
  3. Reset the boiler to see if the error clears and monitoring returns to normal.

Parts commonly replaced

  • External cylinder thermostat
  • Motorised zone valve
  • Secondary heat exchanger

Related codes

D.76

Your boiler is taking a planned temporary break to prevent the burner from switching on and off too frequently, which protects the components from unnecessary wear.

Low DIY-safe

What to check first

  1. Wait for the timer shown on the display to count down to zero
  2. Ensure your room thermostat is turned up to call for heat
  3. Check that radiator valves are open to allow heat to dissipate
D.77

Your boiler is limiting the amount of power it uses to heat your hot water, likely due to a sensor detecting that heat isn't being transferred quickly enough.

Low Engineer only £90-220

Parts commonly replaced

  • NTC Temperature Sensor
  • Secondary Heat Exchanger
  • Diverter Valve

Related codes

D.78

Your boiler is limiting the temperature used to heat your hot water, which usually means it is trying to prevent internal overheating or scale build-up.

Low Engineer only £80-180

Parts commonly replaced

  • NTC Temperature Sensor
  • Heat Exchanger (Descaling)

Related codes

D.80

This is not an error code, but simply a status message on your boiler's screen showing how many hours the heating system has been running.

Low DIY-safe

What to check first

  1. Press the 'i' button to exit the information menu
  2. No action is required as this is an advisory information screen, not a fault

Related codes

D.81

This is a status code rather than a fault, showing you how long the boiler has spent heating your hot water.

Low DIY-safe

What to check first

  1. Press the 'i' button to exit the information menu
  2. Monitor for any actual fault codes if performance is poor
  3. No action is required as this is an advisory information screen

Related codes

D.82

Your boiler is simply indicating that it is starting the process of heating your radiators, which is a normal status message rather than an actual fault.

Low DIY-safe

What to check first

  1. Check if your thermostat is calling for heat
  2. Monitor the display to see if the code changes to a temperature
  3. No action is required as this is a normal operational message

Related codes

D.84

Your boiler is simply reminding you that a routine service is due soon based on its operating hours.

Low Engineer only £80-£120

Parts commonly replaced

  • None (Service only)
  • Burner seal
  • Electrode kit

Related codes

D.90

Your boiler's internal computer is currently processing data or communicating with an external smart thermostat, which is a normal status check and not a hardware failure.

Low DIY-safe £0-80

What to check first

  1. Check your external room thermostat or smart controls are turned up and calling for heat
  2. Wait up to 10 minutes for the digital handshake between the boiler and controls to complete
  3. Reset the boiler using the main power switch if the display remains stuck for over an hour

Parts commonly replaced

  • External Thermostat
  • Low Voltage Wiring
  • PCB

Related codes

Showing 61–70 of 164
D.91

Your boiler is displaying a communication status message regarding an external weather sensor and does not indicate a breakdown.

Low DIY-safe £0-90

What to check first

  1. Check if the outdoor temperature sensor is covered by snow or debris
  2. Observe if the display changes to a temperature reading after a few minutes
  3. Restart the boiler to see if the status cleared

Parts commonly replaced

  • External temperature probe
  • Sensor wiring

Related codes

D.93

Your boiler has lost its internal identity and no longer knows which specific model it is supposed to be, usually following a parts change.

High Engineer only £80-160

Parts commonly replaced

  • Main PCB
  • Display Interface

Related codes

D.96

Your boiler has reverted to its original factory settings and needs its specific configuration data re-entered to work correctly.

Medium Engineer only £80-140

Parts commonly replaced

  • Main PCB
  • Display PCB

Related codes

D.97

Your boiler has entered a specialist programming menu typically used by engineers to change background settings, which means it may not operate as normal until exited.

Low DIY-safe £0-80

What to check first

  1. Press the 'i' or 'back' button to exit the diagnostic menu
  2. Turn the boiler power off and back on again at the fused spur
  3. Press the 'Reset' button if the display does not return to normal status

Parts commonly replaced

  • None (Software setting)
  • Main PCB (if stuck in this mode)

Related codes

D.98

Your boiler has detected a specific internal system fault that requires a professional diagnosis to identify which component has failed.

High Engineer only £120-£350

Parts commonly replaced

  • Main PCB
  • Internal wiring harness
  • External sensor

Related codes

F.00

Your boiler has lost connection to its flow temperature sensor, meaning it cannot accurately monitor the water temperature inside and has shut down as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC Thermistor
  • Wiring harness connection
  • PCB

Related codes

F.00 / F.0

Your boiler has stopped working because it cannot communicate with the internal sensor that monitors the temperature of the water leaving the unit.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC Temperature Sensor
  • Wiring harness/lead
  • Main PCB

Related codes

F.01

Your boiler has stopped working because an internal temperature sensor or its wiring has failed, meaning it can no longer safely monitor the water temperature.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC Thermistor
  • NTC Connection Cable

Related codes

F.1

Your boiler has failed to ignite, which means it cannot provide the heating or hot water you need.

High DIY-safe £90-180

What to check first

  1. Check if your gas supply is active (e.g., check other gas appliances or your meter credit)
  2. Locate the lockout/reset button on the front panel and press it for 2-3 seconds
  3. Ensure the external flue outlet is not obstructed by debris or ice

Parts commonly replaced

  • Ignition electrode
  • Ignition lead
  • Gas valve

Related codes

F.01 / F.1

Your boiler has detected a disconnected or faulty sensor that monitors the water returning to the system, causing the unit to stop working for safety.

High Engineer only £90-£160

Parts commonly replaced

  • NTC Return Temperature Sensor
  • Wiring Harness/Cable Loom

Related codes

Showing 71–80 of 164
F.4

Your boiler is attempting to start but cannot successfully light the gas flame to provide heat or hot water.

High Engineer only £120-£350

Parts commonly replaced

  • Ignition electrode
  • Ignition lead
  • Gas valve
  • PCB

Related codes

F.5

Your boiler has shut down because it grew too hot and reached its safety temperature limit.

High DIY-safe £120-280

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the system pressure is between 1.0 and 1.5 bar
  3. If the boiler is hot, wait 30 minutes for it to cool down and then press the reset button

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • NTC Sensor

Related codes

F.6

Your boiler's internal temperature sensor has stopped sending the correct information to the control board, preventing the system from heating up.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC Thermistor
  • Connecting wiring harness

Related codes

F.10

Your boiler's internal sensor that monitors the flow of water has a loose connection or a wiring fault, causing the system to stop working for safety.

High Engineer only £90-180

Parts commonly replaced

  • Flow NTC sensor
  • Wiring harness
  • Main PCB

Related codes

F.11

Your boiler has detected that water isn't moving through the unit properly, causing it to stop for safety.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the external magnetic filter, if fitted, is not clogged
  3. Check that the boiler pressure is between 1.0 and 1.5 bar on the gauge

Parts commonly replaced

  • Internal Pump
  • Heat Exchanger (Descaling/Flushing)

Related codes

F.12

Your boiler has detected an internal blockage that is preventing water from circulating properly, causing it to stop its heating functions to protect itself.

High Engineer only £180-450

Parts commonly replaced

  • Heat exchanger
  • Internal bypass valve
  • Circulation pump

Related codes

F.13

Your boiler has detected an electrical short circuit in its internal wiring or sensors, preventing it from starting up safely.

High Engineer only £120-280

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring Loom
  • Main PCB

Related codes

F.17

Your boiler has detected an issue with the electrical supply wiring being reversed or a problem with the internal earthing.

High Engineer only £80-160

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

F.20

Your boiler has switched itself off because it has become too hot inside and needs time to cool down before it can restart.

High DIY-safe £90-280

What to check first

  1. Check that all radiator valves are fully open to allow water to flow.
  2. Ensure there is enough pressure in the system by checking the gauge.
  3. Wait for the unit to cool down and press the reset button located on the control panel.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • NTC Temperature Sensor

Related codes

F.21

Your boiler has failed to ignite or stay lit, meaning it cannot provide heating or hot water until the ignition system is fixed.

High Engineer only £120-350

Parts commonly replaced

  • Ignition Lead
  • Spark Electrode
  • Flame Sense Electrode
  • Gas Valve
  • PCB

Related codes

Showing 81–90 of 164
F.22

Your boiler has detected that there is not enough water pressure in the system to operate safely, causing it to shut down to prevent overheating.

High DIY-safe £0-120

What to check first

  1. Check the pressure gauge on the front of the boiler; it should ideally be between 1 and 1.5 bar.
  2. Locate the filling loop (usually a silver flexible hose underneath the boiler).
  3. Slowly open the valves to let water into the system until the gauge reaches the green zone, then close them tightly.
  4. Press the reset button on the boiler control panel.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

Related codes

F.23

Your boiler has shut down because the water is heating up too quickly and the temperature difference between the pipes is too large, usually caused by a circulation problem.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Check the boiler pressure gauge and top up to 1.5 bar if low
  3. Bleed all radiators to remove trapped air
  4. Reset the boiler using the flame symbol or power button

Parts commonly replaced

  • Circulation Pump
  • NTC Temperature Sensors
  • Main Heat Exchanger (if blocked)

Related codes

F.24

Your boiler has stopped working because water is not flowing through the system properly, which is likely caused by a lack of pressure, a pump issue, or a blockage.

High DIY-safe £150-£350

What to check first

  1. Check the pressure gauge on the front of the boiler; if it is below 1.0 bar, top it up to 1.5 bar using the filling loop.
  2. Ensure all radiator valves are fully open to allow water to circulate.
  3. Gently bleed your radiators to remove any trapped air that might be blocking the flow.

Parts commonly replaced

  • Circulation Pump
  • Pressure Sensor
  • Heat Exchanger (De-scaling)

Related codes

F.25

Your boiler has shut down because it detected that the exhaust gases are getting too hot, indicating a potential internal blockage or a circulation problem.

High Engineer only £150-350

Parts commonly replaced

  • Flue Gas NTC Sensor
  • Heat Exchanger
  • Circulation Pump

Related codes

F.26

Your boiler has detected a problem with the gas valve and has shut down as a safety precaution because it cannot correctly manage the flow of fuel.

High Engineer only £180-350

Parts commonly replaced

  • Gas Valve
  • Electronic Control Board (PCB)
  • Wiring Harness

Related codes

F.27

Your boiler thinks it sees a flame even though it hasn't actually started the ignition process, causing it to shut down for safety.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

F.28

Your boiler is failing to light the gas flame required to provide heating and hot water.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances, like a cooker, are working to ensure gas is being supplied to the property.
  2. Ensure your gas meter has credit if you use a pre-payment meter.
  3. Press the reset button (indicated by a flame with a cross through it) for one second to attempt a restart.

Parts commonly replaced

  • Gas Valve
  • Ignition Electrode
  • Ignition Lead
  • PCB

Related codes

F.29

Your boiler has lost its flame while running and cannot stay lit, meaning your heating and hot water will stop working.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances, like a cooker, are working to confirm your gas supply is on.
  2. If you have a prepayment meter, check that you have sufficient credit.
  3. During very cold weather, check if the white plastic condensate pipe leading outside has frozen and gently thaw it with warm water.
  4. Press the reset button (indicated by a flame symbol with a cross) for one second.

Parts commonly replaced

  • Gas Valve
  • Ignition Electrode
  • Flame Sensing Electrode
  • PCB

Related codes

F.32

Your boiler has detected an issue with the fan, meaning it cannot safely clear exhaust gases and will not fire up to provide heat or hot water.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Venturi tube
  • Wiring harness
F.49

Your boiler is having trouble communicating with its internal controls or external thermostat due to an electrical wiring issue.

High Engineer only £100-280

Parts commonly replaced

  • Wiring harness
  • Main PCB
  • eBUS external controls

Related codes

Showing 91–100 of 164
F.60

Your boiler has detected an internal electronic failure that is preventing the gas valve from operating safely, which means your heating and hot water will not work.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Gas Valve Electronic Cable
  • Gas Valve

Related codes

F.61

Your boiler is unable to safely control the gas supply, meaning it cannot ignite to provide heating or hot water.

High Engineer only £180-450

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

F.62

Your boiler has detected a safety issue where the gas valve is not closing properly, which could mean gas is leaking into the burner when it shouldn't be.

Emergency Engineer only £250-450

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

F.63

Your boiler's computer memory has developed a technical fault, preventing it from processing the instructions needed to run properly.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

F.64

Your boiler's internal computer has detected a conflict between its sensors or an electronic error, causing the system to shut down for safety.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • NTC Temperature Sensors
  • Wiring Loom

Related codes

F.65

Your boiler's internal control board has become too hot to function, causing the system to shut down for safety.

High Engineer only £180-350

Parts commonly replaced

  • Main PCB
  • Wiring harness

Related codes

F.67

Your boiler's internal computer is receiving a confused signal from the flame sensor, preventing the system from heating up as a safety precaution.

High Engineer only £180-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Ignition Electrode
  • Flame Sensing Electrode

Related codes

F.68

Your boiler is struggling to keep its flame lit because air has likely mixed with the gas supply or the flame sensor is failing to detect the heat.

High Engineer only £100-£280

Parts commonly replaced

  • Flame Monitoring Electrode
  • Gas Valve
  • Ignition Lead

Related codes

F.70

Your boiler’s control computer has lost its identity settings and no longer recognises which specific model it is supposed to be operating.

High Engineer only £100-£350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Display PCB

Related codes

F.71

Your boiler has detected that a temperature sensor is stuck on a single reading and cannot accurately tell how hot the water is, so it has shut down for safety.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC thermistor
  • Wiring harness
  • Main PCB

Related codes

Showing 101–110 of 164
F.72

Your boiler has detected that the water flowing out is heating up much faster than the returning water, suggesting a sensor fault or a blockage in the system.

High Engineer only £90-180

Parts commonly replaced

  • Flow NTC thermistor
  • Return NTC thermistor
  • Main heat exchanger (cleaning)

Related codes

F.73

Your boiler has detected an issue with its internal pressure sensor, meaning it cannot accurately tell how much water is in the system.

High Engineer only £130-220

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
  • Main PCB

Related codes

F.74

Your boiler's internal sensor has detected an unusual pressure reading and has safely shut down to prevent damage.

High Engineer only £140-£260

Parts commonly replaced

  • Water pressure sensor
  • Sensor wiring harness
  • PCB

Related codes

F.75

Your boiler is failing to start because it cannot detect the necessary rise in water pressure when the internal pump begins to run.

High DIY-safe £180-350

What to check first

  1. Check if your central heating pressure gauge is between 1.0 and 1.5 bar.
  2. If the pressure is too low, use the filling loop to top it up to the correct level.
  3. Restart the boiler to see if the error clears once the system is fully pressurised.

Parts commonly replaced

  • Water pressure sensor
  • Circulation pump
  • Expansion vessel

Related codes

F.76

Your boiler has shut down because a safety sensor has detected that the main component which heats your water has become dangerously hot.

High Engineer only £180-£550

Parts commonly replaced

  • Overheat Termal Fuse
  • Primary Heat Exchanger
  • Main Heat Exchanger Thermal Cut-out

Related codes

F.77

Your boiler has detected a problem with the device that removes wastewater or the flap that seals the exhaust pipe, causing it to shut down for safety.

High Engineer only £120-£250

Parts commonly replaced

  • Condensate pump
  • Flue non-return flap
  • External condensate pipework

Related codes

F.78

Your boiler has lost communication with the hot water temperature sensor, meaning it cannot accurately heat your water for taps and showers.

High Engineer only £90-180

Parts commonly replaced

  • DHW NTC Sensor
  • External Controller Wiring Harness
  • External Control Module

Related codes

F.83

Your boiler is not firing up because it cannot detect a clear change in temperature after it starts the burner.

High DIY-safe £100-220

What to check first

  1. Check that your central heating radiator valves are fully open
  2. Ensure your boiler system pressure is topped up to between 1 and 1.5 bar
  3. Bleed all radiators to remove any trapped air from the system

Parts commonly replaced

  • NTC Temperature Sensors
  • Circulation Pump
  • Heat Exchanger (De-scaling)

Related codes

F.84

Your boiler has noticed that its internal temperature sensors are giving conflicting or illogical readings, which prevents it from heating up safely.

High Engineer only £120-220

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Wiring harness

Related codes

F.85

Your boiler has detected that the temperature sensors are giving unusual readings, likely because they have become loose or were not installed correctly onto the internal pipes.

High Engineer only £90-180

Parts commonly replaced

  • NTC Temperature Sensor
  • Pipe Contact Clips
  • Thermal Paste

Related codes

Showing 111–120 of 164
P.00

Your boiler is currently running an automatic program to clear air bubbles out of the heating and hot water systems.

Low DIY-safe

What to check first

  1. Wait approximately 6 to 10 minutes for the program to finish automatically
  2. Ensure your radiator valves are open to allow air to move through the system
  3. Check the pressure gauge and top up to 1.5 bar if it has dropped after the air was removed

Related codes

P.01

Your boiler is struggling to complete a diagnostic check because it cannot maintain its maximum power level correctly.

Medium Engineer only £100-250

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)
  • Fan

Related codes

P.02

Your boiler is not broken; it is simply running a manual test mode to check how it performs at its lowest power setting.

Low DIY-safe

What to check first

  1. Wait approximately 15 to 20 minutes for the test program to finish automatically
  2. Turn the main power dial or 'Mode' button off and back on to reset the display
  3. Press the 'i' and '+' buttons simultaneously if the code persists

Related codes

P.06

Your boiler is currently running a self-diagnostic test to help fill the central heating system and remove trapped air.

Low DIY-safe

What to check first

  1. Wait approximately 15 minutes for the program to finish automatically
  2. Ensure your radiator valves are open to allow air to be purged
  3. Monitor the pressure gauge to ensure it stays between 1.0 and 1.5 bar

Related codes

S.00

Your boiler is currently on standby because it hasn't received a signal from your thermostat to turn the heating on.

Low DIY-safe £0-£120

What to check first

  1. Check that your room thermostat is turned up higher than the current room temperature
  2. Ensure your heating programmer or timer is set to an 'ON' period
  3. Replace the batteries in your wireless thermostat if the screen is blank

Parts commonly replaced

  • Room thermostat
  • Receiver unit
  • External programmer

Related codes

S.1

Your boiler is unable to start its heating process because the internal fan, which safely clears waste gases, is failing to spin up properly.

High Engineer only £180-450

Parts commonly replaced

  • Fan Assembly
  • Air Pressure Switch
  • PCB (Control Board)

Related codes

S.2

Your boiler is struggling to circulate water properly around the system, which is preventing it from heating up correctly.

High DIY-safe £180-350

What to check first

  1. Check that your boiler pressure is between 1.0 and 1.5 bar on the gauge
  2. Ensure all radiator valves are fully open
  3. Try bleeding your radiators to remove trapped air

Parts commonly replaced

  • Circulating pump
  • Flow pipe sensor

Related codes

S.02

Your boiler is currently preparing to provide heating and is checking that water is moving correctly through the system.

Low DIY-safe £0-120

What to check first

  1. Check that your room thermostat or programmer is set to 'On' and calling for heat
  2. Ensure the radiator valves are open to allow water to circulate
  3. Wait 5-10 minutes as this code often simply indicates a normal pre-heating phase

Parts commonly replaced

  • No parts usually required
  • Circulation pump
  • Diverter valve

Related codes

S.3

Your boiler is struggling to light the burner to provide central heating, meaning your radiators will not warm up.

High DIY-safe £120-350

What to check first

  1. Check that your external gas valve is fully open
  2. If you have a prepay gas meter, ensure you have active credit
  3. Try resetting the boiler by turning the main control dial to 'reset' and back

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Showing 121–130 of 164
S.03

Your boiler is trying to start up to provide heating, but it keeps failing to light the burner successfully.

High DIY-safe £100-£350

What to check first

  1. Check that your gas pre-payment meter (if you have one) has credit.
  2. Verify that other gas appliances in your home, like a hob, are working correctly.
  3. Restart the boiler by turning the main power switch off and back on again.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

S.6

Your boiler is failing to shut down properly after a heating cycle because the internal fan is stuck running for too long.

Medium Engineer only £120-280

Parts commonly replaced

  • Main PCB
  • Fan assembly
  • Air pressure switch

Related codes

S.06

Your boiler is failing to clear leftover gases after a heating cycle because the internal fan is not spinning down as expected.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Air pressure switch

Related codes

S.7

Your boiler has finished its heating cycle but is struggling to circulate water to cool itself down correctly, which can cause the system to pause.

Medium DIY-safe £120-280

What to check first

  1. Ensure all radiator valves (TRVs) are fully open to allow water to circulate
  2. Check that the boiler pressure gauge is between 1 and 1.5 bar
  3. Gently bleed air from the radiators if they feel cold at the top

Parts commonly replaced

  • Circulation Pump
  • Overrun Thermostat
  • Bypass Valve

Related codes

S.07

Your boiler has finished its heating cycle and is now keeping the internal pump running for a short time to safely cool down the internal components.

Low DIY-safe
S.8

Your boiler is temporarily pausing the heating because it has reached its target temperature and is waiting for a short period before restarting to prevent unnecessary wear.

Low DIY-safe

What to check first

  1. Check if your room thermostat is set high enough to call for heat.
  2. Wait up to 15 minutes for the 'anti-cycling' timer to finish.
  3. Ensure all radiator valves are open to allow heat to dissipate.

Related codes

S.08

Your boiler is temporarily resting because it reached its target temperature and is waiting for a short period before restarting to prevent excessive wear.

Low DIY-safe

What to check first

  1. Wait approximately 15 to 20 minutes for the countdown to finish
  2. Ensure your room thermostat is turned up high enough to call for heat
  3. Check that all radiator valves are open to allow heat to dissipate

Related codes

Showing 131–140 of 164
S.11

Your boiler is trying to provide hot water but cannot safely start the internal fan required to clear exhaust fumes.

High Engineer only £180-350

Parts commonly replaced

  • Fan Assembly
  • Air Pressure Switch
  • Venturi Tube

Related codes

S.14

Your boiler is not providing hot water because the internal fan is not spinning fast enough to safely start the heating process.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Venturi tube

Related codes

S.15

Your boiler is briefly keeping the internal fan and pump running to clear away excess heat after you have finished using hot water.

Low DIY-safe
S.16

Your boiler has detected an issue with the fan after you finished using hot water, preventing it from clearing residual gases correctly.

High Engineer only £180-350

Parts commonly replaced

  • Fan motor
  • Air pressure switch
  • Main PCB

Related codes

S.17

Your boiler has finished providing hot water, but the pump is struggling to circulate the remaining heat away from the system, likely due to a blockage or a valve issue.

Medium Engineer only £120-280

Parts commonly replaced

  • Three-way diverter valve
  • Circulating pump
  • Heat exchanger

Related codes

S.20

Your boiler has received a request to provide hot water, but it is taking longer than expected to start the heating process.

Low DIY-safe £0-120

What to check first

  1. Check that your hot water taps are fully turned off
  2. Turn the boiler power off and back on again to reset the sequence
  3. Ensure there is enough water pressure showing on the gauge (between 1.0 and 1.5 bar)

Parts commonly replaced

  • None (usually a status message)
  • Diverter valve
  • Flow sensor

Related codes

S.21

Your boiler is trying to provide hot water, but the internal fan that clears away waste gases is failing to start up properly.

High Engineer only £180-£350

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Main PCB

Related codes

S.22

Your boiler has detected that water isn't moving through the system properly while trying to provide hot water.

High Engineer only £180-350

Parts commonly replaced

  • Circulation pump
  • Secondary heat exchanger
  • Diverter valve

Related codes

S.23

Your boiler is failing to light the burner when you turn on your hot water tap.

High Engineer only £120-300

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensor

Related codes

S.24

Your boiler is simply letting you know that it is currently busy heating up water for your taps.

Low DIY-safe

What to check first

  1. Check if a hot water tap is currently turned on elsewhere in the house
  2. Ensure any mixer showers are fully turned off
  3. Monitor the display to see if the code changes once the tap is closed

Related codes

Showing 141–150 of 164
S.25

Your boiler is pausing after a period of providing hot water because it has detected an issue with the internal cooling process involving the pump or fan.

Medium DIY-safe £120-280

What to check first

  1. Check that all radiator valves and internal bypass valves are open to ensure water flow.
  2. Reset the boiler using the main power switch or reset button.
  3. Check that there are no external obstructions to the flue terminal outside.

Parts commonly replaced

  • Circulation Pump
  • Fan Assembly
  • PCB

Related codes

S.26

Your boiler is briefly cooling itself down after you have used the hot water, which is a normal part of its operation.

Low DIY-safe

What to check first

  1. No action is required as this is a status code, not a permanent error.
  2. Wait for the fan to stop spinning naturally once the internal temperature drops.
  3. Ensure your hot water taps are fully closed.

Related codes

S.27

Your boiler is temporarily running the internal pump after you have turned off the hot tap to help the system cool down safely.

Low DIY-safe
S.28

Your boiler is temporarily pausing the burner to prevent it from switching on and off too frequently while heating your water.

Low DIY-safe

What to check first

  1. Wait for 10 to 15 minutes for the anti-cycle timer to finish
  2. Ensure hot water taps are fully turned off
  3. Check that the boiler pressure is between 1 and 1.5 bar on the gauge

Related codes

S.30

Your boiler is working fine, but your wall thermostat is currently telling it to stay switched off because your home is already at the desired temperature.

Low DIY-safe £0-£120

What to check first

  1. Check if your wall thermostat is set to a lower temperature than the room currently is.
  2. Turn up the temperature on your room thermostat or programmer to see if the boiler fires up.
  3. Replace the batteries in your wireless room thermostat if the display is blank or fading.

Parts commonly replaced

  • Room thermostat batteries
  • Wall thermostat unit
  • External programmer

Related codes

S.31

Your boiler is currently set to summer mode, which means it is ignoring the thermostat and will only provide hot water, not heating.

Low DIY-safe

What to check first

  1. Locate the radiator temperature dial on the front of the boiler control panel.
  2. Turn the dial clockwise to the desired temperature setting to enable central heating.
  3. Ensure your wall thermostat is turned up and calling for heat.

Related codes

S.32

Your boiler is temporarily pausing because the fan is not spinning at the correct speed needed to safely clear exhaust fumes.

High Engineer only £180-450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Air pressure switch

Related codes

S.34

Your boiler has entered a temporary frost protection mode to prevent internal pipes from freezing due to very low temperatures.

Low DIY-safe £0-80

What to check first

  1. Check that your home heating is turned on at the thermostat
  2. Ensure any radiator valves in the room with the boiler are fully open
  3. Wait for the boiler to warm up naturally as the code should vanish once the temperature rises

Parts commonly replaced

  • External NTC temperature sensor
  • Printed Circuit Board (PCB)

Related codes

S.36

Your boiler is currently set to a mode where it isn't asking for heat because it doesn't think any is needed based on your external controls.

Low DIY-safe £0-120

What to check first

  1. Check that your room thermostat is turned up higher than the current room temperature.
  2. Ensure your programmer or heating timer is set to 'ON'.
  3. Replace the batteries in your wireless wall thermostat if it has an empty display.

Parts commonly replaced

  • External Room Thermostat
  • Wiring Centre
  • Control PCB

Related codes

S.39

Your boiler has temporarily stopped heating because a safety sensor or an external pump has detected an issue and cut the power to the burner.

Medium DIY-safe £90-220

What to check first

  1. Check if your condensate pump (if you have one) is plugged in and turned on.
  2. Ensure the pipe leading from the condensate pump to the outside or drain is not blocked or frozen.
  3. Reset the boiler by turning it off and on again to see if the status clears.

Parts commonly replaced

  • Condensate pump
  • Contact thermostat
  • Wiring harness

Related codes

Showing 151–160 of 164
S.40

Your boiler has detected an internal issue and is running at a lower power level to keep providing some heat while protecting itself from damage.

Medium DIY-safe £120-280

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar
  3. Press the 'Reset' button (flame symbol with a cross) and wait for the boiler to restart

Parts commonly replaced

  • Temperature sensors (NTC thermistors)
  • Primary heat exchanger
  • Central heating pump

Related codes

S.41

Your boiler has stopped working because the water pressure inside the system is too high.

High DIY-safe £0-120

What to check first

  1. Check that the internal or external filling loop valves are fully closed.
  2. Turn off the boiler and allow the system to cool down.
  3. Bleed water from a radiator using a bleed key to reduce the pressure.
  4. Monitor the pressure gauge until it returns to between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve

Related codes

S.42

Your boiler has paused operation because a safety flap in the flue system is stuck or sending an incorrect signal, preventing waste gases from being cleared safely.

High Engineer only £120-£280

Parts commonly replaced

  • Flue non-return flap
  • Fan assembly
  • Flow/Return sensors

Related codes

S.46

Your boiler is struggling to maintain a small flame when it tries to run at its lowest power setting, causing it to shut down for safety.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation electrode
  • Gas valve
  • Burner

Related codes

S.53

Your boiler has temporarily paused because it is struggling to move enough water through the system, likely due to low pressure or a blockage.

High DIY-safe £90-250

What to check first

  1. Check the pressure gauge and top up to 1.5 bar if it is low
  2. Ensure all radiator valves are fully open
  3. Bleed your radiators to remove trapped air
  4. Reset the boiler to see if the code clears

Parts commonly replaced

  • Central heating pump
  • Main heat exchanger (flushing)
  • Pressure sensor

Related codes

S.54

Your boiler has temporarily paused its operation because it has detected a problem with getting water through the system quickly enough.

High DIY-safe £100-£350

What to check first

  1. Check that all radiator valves (TRVs) are fully open
  2. Ensure the boiler pressure gauge is within the green zone (usually 1.0 to 1.5 bar)
  3. Check for any visible leaks around the pipework or radiators

Parts commonly replaced

  • Circulation Pump
  • Secondary Heat Exchanger
  • Return Flow Thermistor

Related codes

S.57

Your boiler is temporarily pausing to prevent overheating after reaching a high temperature, often due to a lack of proper water flow.

Medium DIY-safe £90-250

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar on the gauge
  3. Wait up to 15 minutes for the 'comfort' delay period to end automatically

Parts commonly replaced

  • Circulation Pump
  • Central Heating Filter
  • Heat Exchanger (Descaling)

Related codes

S.58

Your boiler is temporarily limiting its power because strong wind or a blockage is interfering with how the flames burn.

Low DIY-safe £90-180

What to check first

  1. Check the external flue terminal for obstructions like debris or nests
  2. Monitor the boiler as this status usually clears automatically when wind speed drops
  3. If the code persists during calm weather, book a Gas Safe engineer to inspect the fan and flue

Parts commonly replaced

  • Flue terminal
  • Fan
  • Gas valve

Related codes

S.61

Your boiler has failed an internal test to identify the specific type of gas being supplied, which has caused it to stop running for safety.

High Engineer only £180-450

Parts commonly replaced

  • Gas valve
  • Detection electrode
  • Printed Circuit Board (PCB)

Related codes

S.85

Your boiler is struggling to move enough water through the system to operate safely and effectively.

Medium DIY-safe £100-280

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar
  3. Check if any bypass valves in your heating system are closed

Parts commonly replaced

  • Circulation pump
  • Water pressure sensor
  • Main heat exchanger (de-scaling)

Related codes

Showing 161–164 of 164
S.96

Your boiler has detected a problem with the sensor that monitors water temperature returning from your radiators, preventing it from heating your home efficiently.

High Engineer only £90-160

Parts commonly replaced

  • Return NTC thermistor
  • Wiring harness
  • Main PCB

Related codes

S.98

Your boiler is temporarily pausing to double-check its internal sensors to ensure the temperature readings are accurate before starting up.

Low Engineer only £90-180

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Wiring harness

Related codes

S.O

Your boiler is currently in standby mode because it hasn't received a signal from your thermostat to turn the heating on.

Low DIY-safe £0-120

What to check first

  1. Check that your room thermostat is turned up higher than the current room temperature
  2. Ensure your heating programmer or timer is set to 'ON'
  3. Replace the batteries in your wireless thermostat if the screen is blank

Parts commonly replaced

  • Thermostat batteries
  • Room thermostat
  • External programmer

Related codes

S13

Your boiler is struggling to light the flame specifically when you turn on your hot water taps.

High Engineer only £120-280

Parts commonly replaced

  • Ignition Electrodes
  • Gas Valve
  • DHW Flow Switch
  • Printed Circuit Board (PCB)