Worcester Bosch 26 CDi Xtra Fault codes & diagnostics

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

Combi Natural Gas 26 kW 1997-2005 Discontinued
GC Number 47-311-39

Replaced by: CDi Classic

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
5 Emergency 117 High 4 Medium 30 Low

All 156 documented codes

Tap any card for details

Fast flash

Your boiler has detected a critical internal communication or hardware error and has locked itself out for safety.

High Engineer only £180-450

Parts commonly replaced

  • Fan
  • Printed Circuit Board (PCB)
  • Code Plug

Related codes

2 pulses

Your boiler has been manually set to run at its lowest power level for testing, which prevents it from heating your home normally.

Low DIY-safe £0-80

What to check first

  1. Locate the service mode switch or dial on the control panel
  2. Ensure the switch is turned back to the 'Normal' or 'Off' position rather than the 'Min' setting
  3. Press the reset button to clear the flashing light

Parts commonly replaced

  • None (Adjustment only)
  • Control Knob
5 pulses

Your boiler has been left in a manual testing mode, usually used by engineers during a service, which is preventing it from running normally.

Medium DIY-safe £0-80

What to check first

  1. Locate the control panel on the front of the boiler.
  2. Find the small white service switch (often marked with a flame or 'Max').
  3. Ensure the switch is moved back to the 'Normal' or 'Off' position rather than 'Max'.
9A 361

Your boiler's internal computer parts do not recognise each other and are unable to communicate, preventing the heating from starting.

High Engineer only £180-£450

Parts commonly replaced

  • Burner Control Unit (PCB)
  • KIM (Boiler Identification Module)

Related codes

9A 362

Your boiler’s internal computer chip is either loose or is the wrong version for this specific model, causing the system to shut down for safety.

High Engineer only £140-£280

Parts commonly replaced

  • Heatcom Chip (HCM)
  • Main Printed Circuit Board (PCB)

Related codes

9U 233

Your boiler has developed a communication fault with its internal identity chip, meaning it no longer recognizes its own settings and cannot operate.

High Engineer only £140-£260

Parts commonly replaced

  • Code Plug
  • Printed Circuit Board (PCB)
200

Your boiler is simply letting you know that it is currently operating and working to heat your home's radiators.

Low DIY-safe

What to check first

  1. No action is required as this is an advisory status code, not a fault.
  2. Check your thermostat settings if the heating is on when you do not want it to be.
  3. Wait for the heating cycle to finish for the code to change.

Related codes

201

Your boiler is simply indicating that it is currently busy heating your hot water, which is a normal operating status rather than a breakdown.

Low DIY-safe

What to check first

  1. Check if a hot water tap is turned on somewhere in the house
  2. Close any open hot water taps to allow the boiler to return to heating mode
  3. Verify that the pre-heat function is not simply running a routine cycle

Related codes

201 O

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. No action is required as this is a status code, not an error.
  2. The code will disappear once you turn off the hot water tap.

Related codes

Showing 11–20 of 156
202

Your boiler is working normally and is simply waiting for a signal from your thermostat to start heating.

Low DIY-safe

What to check first

  1. Check that your room thermostat is turned up high enough to call for heat.
  2. Ensure the batteries in your wireless thermostat are still working.
  3. Verify that the heating timer or programmer is set to 'On' or 'Auto'.

Related codes

202 O

Your boiler is taking a brief programmed rest to prevent itself from switching on and off too frequently, which protects the internal components from unnecessary wear.

Low DIY-safe

What to check first

  1. Check if your room thermostat is set too low and increase it slightly if needed
  2. Open any closed radiator valves to ensure heat can move away from the boiler
  3. Wait 15-20 minutes for the 'anti-cycle' timer to expire and the boiler to restart automatically

Related codes

203

Your boiler is currently sitting in a normal standby mode because there is no demand for heating or hot water at the moment.

Low DIY-safe

What to check first

  1. Check that your room thermostat or programmer is turned up higher than the current room temperature.
  2. Ensure the heating timer is set to an 'ON' period.
  3. Try turning on a hot water tap to see if the boiler fires up.

Related codes

203 0

Your boiler is working correctly and is simply waiting for you to turn up the thermostat or run a hot tap to start heating.

Low DIY-safe

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. Check that your thermostatic radiator valves are turned up

Related codes

204

Your boiler is temporarily pausing because it has already reached the required temperature and is waiting for the water to cool down slightly before firing up again.

Low DIY-safe

What to check first

  1. Check that your room thermostat is set to the desired temperature
  2. Open the radiator valves in key rooms to allow heat to dissipate
  3. Wait for the boiler to restart automatically once the water temperature drops

Related codes

204 O

Your boiler has temporarily stopped because the water inside it has become hotter than the temperature you have requested.

Low DIY-safe £0-120

What to check first

  1. Check that your radiator valves are fully open to allow heat to circulate
  2. Ensure the boiler thermostat dial is not set to maximum
  3. Wait for the boiler to cool down naturally, as the code often clears itself

Parts commonly replaced

  • No parts usually required
  • Temperature Sensor (NTC Thermistor)

Related codes

208

Your boiler is currently running in a manual testing mode used by engineers to check emissions, which overrides your normal temperature settings.

Low DIY-safe £0-80

What to check first

  1. Locate the button with a 'chimney sweep' or 'flame' icon on the control panel.
  2. Press and hold the button for at least five seconds until the display returns to the normal temperature reading.
  3. Switch the boiler power off and back on at the fused spur switch to reset the software if the code persists.

Related codes

208 0

Your boiler is currently set to a manual testing mode used by engineers to check emissions and is not experiencing an actual part failure.

Low DIY-safe

What to check first

  1. Locate the 'Chimney Sweep' button (symbol looks like a small brush or a circle within a triangle) on the control panel.
  2. Press and hold the button for at least 5 seconds until the display returns to the normal temperature reading.
  3. Switch the boiler off and back on at the fused spur switch to reset the operating mode.

Related codes

212

Your boiler has detected that the water inside is heating up too fast, causing it to shut down to prevent damage from overheating.

High 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 and 1.5 bar
  3. Try resetting the boiler if the system has had time to cool down

Parts commonly replaced

  • Circulation Pump
  • Flow Temperature Sensor (NTC)
  • Safety Limit Thermistor

Related codes

224 V

Your boiler has switched itself off because it has detected it is getting too hot, likely because the water pressure is too low.

High DIY-safe £0-120

What to check first

  1. Locate the internal or external filling loop (usually two blue levers or a white key underneath the boiler).
  2. Slowly open the valves to top up the water pressure until the needle on the gauge reaches between 1 and 1.5 bar.
  3. Press the 'Reset' button on the front control panel to restart the boiler.

Parts commonly replaced

  • Overheat Thermostat
  • Filling Loop
  • System Pressure Sensor

Related codes

Showing 21–30 of 156
226

Your boiler is displaying a status message indicating that a technician's diagnostic tool has recently accessed the system's error history memory.

Low DIY-safe £0-80

What to check first

  1. Press and hold the 'Reset' button for five seconds
  2. Wait for the boiler to restart and complete its self-test
  3. If the code persists, cycle the power to the boiler off and on at the fused spur switch

Parts commonly replaced

  • None (Software status code)

Related codes

227 V

Your boiler is trying to light, but the internal system is failing to detect a flame, causing the unit to shut down for safety.

High DIY-safe £120-£350

What to check first

  1. Check if your gas supply is active by testing other gas appliances like a hob
  2. Ensure your gas meter has credit if you use a prepay meter
  3. Briefly press the reset button once to see if the system restarts

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

228 V

Your boiler thinks it sees a flame even though it isn't actually firing, which is preventing it from starting up safely.

High Engineer only £160-£350

Parts commonly replaced

  • Ionisation Lead
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

235

Your boiler’s internal computer and control module are not communicating correctly because their software versions do not match.

High Engineer only £180-350

Parts commonly replaced

  • Heat Control Module (HCM)
  • PCB (Printed Circuit Board)
260

Your boiler is starting up, but it is turning itself off quickly because it cannot detect your water getting any warmer.

High DIY-safe £100-280

What to check first

  1. Check that all your radiator valves are fully open
  2. Check that the boiler pressure is between 1 and 1.5 bar on the front gauge
  3. Switch the boiler off and back on again to see if the fault clears

Parts commonly replaced

  • Circulating Pump
  • Flow Temperature Sensor (NTC)
  • Main Heat Exchanger (if blocked)

Related codes

265

Your boiler is temporarily reducing its output because it has reached its target temperature and is waiting for the system to cool down before firing up fully again.

Low DIY-safe £0-120

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the room thermostat is turned up higher than the current room temperature
  3. Check if the system pressure gauge is between 1 and 1.5 bar

Parts commonly replaced

  • External heating controls
  • System bypass valve

Related codes

268

Your boiler is currently running a self-diagnostic check of its internal parts, which it usually does automatically.

Low DIY-safe

What to check first

  1. Wait for the boiler to complete its automatic test cycle.
  2. If the code persists, try resetting the boiler.
  3. Ensure there is power to the unit and the system pressure is adequate.

Related codes

283

Your boiler is simply performing its normal startup sequence and testing internal components before the flame ignites.

Low DIY-safe

What to check first

  1. Wait up to 2 minutes for the boiler to complete its self-test and fire up
  2. Monitor the display to see if the code clears and heating begins
  3. If the code stays on for a long period, try resetting the boiler once

Related codes

284

Your boiler has detected an internal communication error involving the gas control components, meaning it cannot safely ignite.

High Engineer only £150-£350

Parts commonly replaced

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

Related codes

Showing 31–40 of 156
305

Your boiler is temporarily paused because it thinks hot water is still being used elsewhere in your home.

Low DIY-safe £90-180

What to check first

  1. Ensure all hot water taps and showers are fully turned off.
  2. Check for any dripping taps or leaking hot water pipes.
  3. Turn the boiler off and back on at the fused spur switch to reset the sensor.

Parts commonly replaced

  • DHW Flow Turbine
  • Flow Sensor
  • Diverter Valve
305 0

Your boiler is temporarily pausing the hot water production to prevent the system from overheating and will restart automatically in a few minutes.

Low DIY-safe

What to check first

  1. Wait 5 to 10 minutes for the anti-cycle timer to finish
  2. Ensure hot water taps are fully closed
  3. Check if the hot water temperature dial is set unnecessarily high and turn it down slightly

Related codes

306 V

Your boiler is still detecting a flame even though it has tried to shut off the gas supply, which is a safety conflict.

Emergency Engineer only £280-450

Parts commonly replaced

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

Related codes

328

Your boiler has detected an issue with the electrical power supply it is receiving, meaning the electricity frequency is unstable and the system has shut down for protection.

High Engineer only £180-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Mains voltage protector

Related codes

356

Your boiler has detected that the incoming electricity supply is too weak or unstable to run the system safely.

High Engineer only £100-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Transformer
360

Your boiler's computer brains are having a communication problem because an incorrect or faulty internal component has been detected.

High Engineer only £180-350

Parts commonly replaced

  • Heat Control Module (HCM)
  • Main PCB

Related codes

360 V

Your boiler's internal computer chip is either loose or is not the correct one designed for this specific model, preventing the system from running.

High Engineer only £120-£250

Parts commonly replaced

  • HCM Code Plug
  • Boiler PCB (Printed Circuit Board)
815 W/B

Your boiler has detected a problem with a temperature sensor that monitors how water is circulating through the system, which is preventing it from heating up correctly.

High Engineer only £120-£220

Parts commonly replaced

  • Low loss header temperature sensor
  • NTC thermistor
  • Wiring harness
1010 O

Your boiler has lost its internal connection to the smart controls or main computer system, meaning it cannot receive instructions to provide heating or hot water.

High Engineer only £100-280

Parts commonly replaced

  • EMS Bus Wiring Loom
  • Fuse
  • Main PCB

Related codes

1017 W

Your boiler has detected that the water pressure is too low for it to operate safely and needs to be refilled.

High DIY-safe £0-160

What to check first

  1. Locate the internal or external filling loop (usually blue levers or a silver braided hose under the boiler)
  2. Slowly open the valves until you hear water flowing
  3. Close the valves once the pressure gauge reaches between 1.0 and 1.5 bar

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Automatic air vent

Related codes

Showing 41–50 of 156
1021 B

Your boiler is struggling to provide hot water because the internal sensor that monitors water temperature has stopped working or has come loose.

High Engineer only £90-160

Parts commonly replaced

  • DHW Temperature Sensor (NTC Thermistor)
  • Wiring harness connector

Related codes

1022 B

Your boiler is unable to tell how hot your water is because of a faulty or disconnected internal sensor.

High Engineer only £90-180

Parts commonly replaced

  • Hot water NTC temperature sensor
  • Wiring harness

Related codes

1037 W

Your boiler's outdoor sensor is faulty or has a loose connection, which may affect how efficiently the system manages your heating based on the weather.

Low Engineer only £90-160

Parts commonly replaced

  • Weather compensation sensor
  • Sensor wiring
1065 B

Your boiler's internal pressure monitor has stopped communicating correctly with the main controls, which will prevent the heating from running.

High Engineer only £140-£260

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
  • PCB (Main control board)

Related codes

1068 W

Your boiler's outdoor weather sensor is not communicating correctly, which means the system doesn't know how hard it needs to work to heat your home.

Low Engineer only £90-180

Parts commonly replaced

  • Outdoor weather compensation sensor
  • Sensor wiring harness

Related codes

1073 W

Your boiler has detected an electrical fault with its internal thermometer, meaning it cannot safely monitor the water temperature and has stopped working as a precaution.

High Engineer only £90-160

Parts commonly replaced

  • Flow temperature sensor (NTC thermistor)
  • Connecting wiring harness

Related codes

1074 W

Your boiler has lost communication with its internal thermometer, which means it cannot tell how hot the water is getting and has stopped working for safety.

High Engineer only £90-180

Parts commonly replaced

  • Flow Temperature Sensor (NTC Thermistor)
  • Wiring Harness
  • Main PCB

Related codes

1075 W

Your boiler has detected an electrical fault with an internal temperature sensor, meaning it cannot monitor heat levels safely and has shut down to prevent damage.

High Engineer only £90-£160

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring Harness

Related codes

1076 W

Your boiler has stopped working because it cannot communicate with the internal heat sensor and has shut down for safety.

High Engineer only £100-280

Parts commonly replaced

  • NTC Temperature Sensor
  • Sensor Wiring Harness
  • Main PCB

Related codes

2920 V

Your boiler has detected an issue with the flame and has shut down as a safety precaution to ensure gas is not being supplied without being burned.

High Engineer only £120-£350

Parts commonly replaced

  • Ionisation Probe
  • Flame Sensing Electrode
  • Ignition Lead
  • Printed Circuit Board (PCB)

Related codes

Showing 51–60 of 156
2924 V

Your boiler's internal control system has lost communication with the gas supply valve, meaning the boiler cannot safely ignite to provide heating or hot water.

High Engineer only £280-450

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

2925 V

Your boiler is struggling to supply the correct amount of gas required to maintain a steady flame, causing the system to shut down for safety.

High Engineer only £180-£350

Parts commonly replaced

  • Modulating Gas Valve
  • Spark Electrodes
  • Printed Circuit Board (PCB)

Related codes

2927 B

Your boiler has lost its flame while it was running and cannot stay lit to provide heating or hot water.

High DIY-safe £120-450

What to check first

  1. Check that your gas emergency control valve is in the 'on' or 'open' position
  2. If you have a pre-payment meter, ensure it has sufficient credit
  3. Try resetting the boiler by holding the reset button for five seconds

Parts commonly replaced

  • Ionisation electrode
  • Gas valve
  • Burner control unit (PCB)

Related codes

2946 V

Your boiler has an internal configuration part that is either damaged or incompatible, which is preventing the system from running safely.

High Engineer only £120-220

Parts commonly replaced

  • HCM (Heating Control Module) Code Plug
  • Printed Circuit Board (PCB)

Related codes

2948 B

Your boiler is struggling to detect a flame when starting up, meaning it may fail to provide consistent heating or hot water.

High Engineer only £120-350

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve
  • PCB

Related codes

2950 B

Your boiler is failing to detect a flame after trying to start, which means it will not provide heating or hot water until it is reset or repaired.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation probe
  • Ignition electrode
  • Gas valve
  • Burner gasket

Related codes

2963 B

Your boiler has stopped working because its internal sensors are sending conflicting information about the water temperature.

High Engineer only £120-£240

Parts commonly replaced

  • Flow temperature sensor
  • Heat exchanger NTC sensor
  • Wiring harness

Related codes

2964 B

Your boiler has detected that water isn't moving through the system fast enough to safely carry heat away, so it has shut down to prevent overheating.

High DIY-safe £120-£350

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 for any visible leaks around the pipework or radiators

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger (Flushing)
  • Flow Temperature Sensor

Related codes

2965 B

Your boiler has sensed that the water inside is Getting too hot and has shut itself down as a safety precaution.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure there is enough water pressure in the system (usually between 1 and 1.5 bar on the gauge)
  3. Press the reset button once the boiler has had time to cool down

Parts commonly replaced

  • Circulation pump
  • Heat exchanger
  • Temperature thermistor (NTC sensor)

Related codes

2966 B

Your boiler is heating up too quickly and has shut down to prevent damage, usually because water isn't moving through the system properly.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure your system pressure is between 1.0 and 1.5 bar
  3. Reset the boiler using the reset button

Parts commonly replaced

  • Circulation pump
  • Main heat exchanger (flushing/cleaning)
  • Flow temperature sensor

Related codes

Showing 61–70 of 156
2967 B

Your boiler has detected that the water temperature is changing too quickly or unevenly between different sensors, causing it to shut down for safety.

High Engineer only £120-280

Parts commonly replaced

  • Flow temperature sensor
  • Heat exchanger
  • Main circulator pump

Related codes

2970 B

Your boiler has detected that the water pressure in your heating system is falling much too quickly, which usually means there is a significant leak or a fault with the pressure sensor.

High DIY-safe £80-250

What to check first

  1. Check all visible pipework and radiators for signs of water leaks
  2. Use the internal filling link or external valves to top up the system pressure to 1.5 bar
  3. Monitor the pressure gauge to see if it drops again immediately
  4. Ensure all radiator bleed valves are tightly closed

Parts commonly replaced

  • Pressure Sensor
  • Expansion Vessel
  • Pressure Relief Valve

Related codes

2971 B

Your boiler has detected that the water pressure in your heating system is too low to operate safely.

High DIY-safe £120-220

What to check first

  1. Locate the filling loop (the silver braided hose beneath the boiler).
  2. Slowly open the valves to let water into the system while watching the pressure gauge.
  3. Close the valves once the pressure reaches between 1 and 1.5 bar.

Parts commonly replaced

  • Pressure sensor
  • Wiring harness

Related codes

A1

Your boiler has detected that there isn't enough water moving through the system, which is usually caused by a leak or a pump that has stopped working.

High DIY-safe £180-£350

What to check first

  1. Check for any visible water leaks around the boiler or radiators
  2. Check your pressure gauge and top it up to 1.5 bar using the filling link if it is low
  3. Restart the boiler to see if the pump clears itself

Parts commonly replaced

  • Circulation Pump
  • Expansion Vessel
  • Auto Air Vent

Related codes

A1 281

Your boiler's internal pump is unable to circulate water because it is either physically jammed or there is too much trapped air inside the system.

High DIY-safe £120-£320

What to check first

  1. Check that your system pressure is between 1 and 1.5 bar on the pressure gauge.
  2. Try bleeding your radiators to release any trapped air from the system.
  3. Reset the boiler by holding the reset button for five seconds to see if the pump restarts.

Parts commonly replaced

  • Circulating Pump
  • Automatic Air Vent
  • Pump Capacitor

Related codes

A3 317

Your boiler has detected a faulty connection or a broken sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety.

High Engineer only £120-£200

Parts commonly replaced

  • Flue Gas Temperature Sensor (NTC)
  • Wiring harness / connector

Related codes

A7

Your boiler's hot water sensor has failed or has a loose connection, meaning the system cannot accurately measure the temperature of the water coming out of your taps.

Medium Engineer only £90-160

Parts commonly replaced

  • Hot water NTC sensor
  • Wiring harness

Related codes

A8

Your boiler has lost its connection with your external heating controls, meaning it cannot receive instructions on when to turn on or off.

High Engineer only £80-220

Parts commonly replaced

  • External room thermostat
  • Wiring harness
  • Receiver unit

Related codes

A8 362

Your boiler is receiving an unstable or incorrect electrical supply, which is preventing it from running safely.

High Engineer only £180-450

Parts commonly replaced

  • Heat Control Module (HCM)
  • Main Printed Circuit Board (PCB)
  • External Power Supply Connection

Related codes

Air Pressure Fault

Your boiler is struggling to clear exhaust fumes or draw in fresh air, so it has safely shut down to prevent any risk.

High Engineer only £150-300

Parts commonly replaced

  • Air pressure switch
  • Fan assembly
  • Venturi
  • Flue seals

Related codes

Showing 71–80 of 156
B1

Your boiler's main control board cannot communicate with the internal configuration chip, meaning the system doesn't know which settings to use and has stopped working.

High Engineer only £120-£350

Parts commonly replaced

  • HCM Code Plug
  • Printed Circuit Board (PCB)
B7 257

Your boiler's internal computer has encountered an electronic failure and cannot safely operate the heating or hot water.

High Engineer only £280-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Electronic Control Unit

Related codes

Burner Lockout

Your boiler has failed to light the flame properly and has turned itself off for safety, meaning you currently have no heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrodes
  • Gas valve
  • Flame rectification probe

Related codes

C1 264

Your boiler has shut down because it has detected a problem with the fan or the way air is moving through the system while it was running.

High Engineer only £150-350

Parts commonly replaced

  • Fan
  • Air Pressure Switch
  • Venting/Flue seals
  • Printed Circuit Board (PCB)

Related codes

C4 237

Your boiler's internal computer has suffered an electrical failure and can no longer control the heating process safely.

High Engineer only £280-£450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Heat Control Module (HCM)

Related codes

C4 273

Your boiler has detected a small airflow issue while running its daily safety self-test, often meaning it needs a professional service or a minor part cleaned.

Low Engineer only £90-180

Parts commonly replaced

  • Fan
  • Air pressure switch
  • Venturi tube

Related codes

C6

Your boiler has stopped working because the internal fan, which safely clears exhaust gases, isn't spinning fast enough.

High Engineer only £220-£450

Parts commonly replaced

  • Fan assembly
  • Fan wiring harness
  • Main PCB

Related codes

C6 215

Your boiler has stopped working because the fan is spinning at the wrong speed, which means the system cannot safely clear exhaust gases.

High Engineer only £250-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness
C6 216

Your boiler has stopped working because the internal fan that clears away waste gases is spinning too slowly or is stuck.

High Engineer only £180-£350

Parts commonly replaced

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

Related codes

C7 214

Your boiler has stopped working because the fan that clears out exhaust gases is unable to start or run properly.

High Engineer only £250-£450

Parts commonly replaced

  • Fan Assembly
  • Printed Circuit Board (PCB)
  • Air Pressure Switch

Related codes

Showing 81–90 of 156
C7 216

Your boiler has stopped working because the internal fan isn't spinning fast enough to safely clear away exhaust fumes.

High Engineer only £180-£450

Parts commonly replaced

  • Fan Assembly
  • Wiring Harness
  • Main PCB

Related codes

C7 217

Your boiler has shut down because the internal fan, which safely clears waste gases from the system, has suddenly stopped working while the boiler was running.

High Engineer only £250-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

CC 800

Your boiler has lost connection with its outdoor temperature sensor, which means it cannot adjust its settings based on the weather outside.

Low DIY-safe £90-180

What to check first

  1. Check for any visible damage to the sensor or wiring on your home's outside wall
  2. Switch the boiler off and back on again to see if the error clears
  3. Check if the batteries needs replacing if it is a wireless sensor model

Parts commonly replaced

  • Outdoor weather compensation sensor
  • Sensor wiring

Related codes

CE 207

Your boiler has stopped working because there is not enough water pressure in the system to operate safely.

High DIY-safe £0-120

What to check first

  1. Locate the internal or external filling loop (usually a silver braided hose with small valves below the boiler).
  2. Slowly open the valve(s) until you hear water entering the system.
  3. Watch the pressure gauge and close the valves tightly once the needle reaches between 1 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

CE 266

Your boiler has stopped working because it has detected that the internal pump is not moving water through the system correctly.

High Engineer only £220-£450

Parts commonly replaced

  • Central heating pump
  • Main PCB
  • Pump cable

Related codes

D1 240

Your boiler has detected a problem with the sensor that monitors water returning to the unit, meaning it cannot safely track temperature levels.

High Engineer only £90-160

Parts commonly replaced

  • Return thermistor (NTC sensor)
  • Wiring harness connecting to the sensor

Related codes

D1 241

Your boiler has stopped working because it has lost a connection with one of its internal heat sensors.

High Engineer only £90-160

Parts commonly replaced

  • Return Temperature Sensor (NTC Thermistor)
  • Wiring Harness
  • Main PCB

Related codes

D3 232

An external safety device or thermostat has signaled the boiler to stop running, often due to an issue like a full condensate pump or a tripped safety switch.

High DIY-safe £100-220

What to check first

  1. Check if your thermostat or programmer has power and is calling for heat.
  2. If you have a condensate pump (a small plastic box near the boiler), check if it is full of water or blocked.
  3. Ensure any external emergency 'stop' switches have not been accidentally knocked.

Parts commonly replaced

  • External Condensate Pump
  • Wiring Link/Bridge
  • Room Thermostat
D4 213

Your boiler is overheating because the water inside it is getting too hot much faster than it should be.

High DIY-safe £120-350

What to check first

  1. Check that your radiator valves (TRVs) are turned up and not all closed.
  2. Ensure your system pressure is between 1 and 1.5 bar on the pressure gauge.
  3. Check if any of your bypass valves are fully open.

Parts commonly replaced

  • Circulating pump
  • Flow temperature sensor (NTC)
  • Main heat exchanger (de-scaling)

Related codes

D4 271

Your boiler is shutting down because it has detected a sudden rise in temperature or a lack of water flow, often caused by a blockage or air trapped in the system.

High DIY-safe £120-350

What to check first

  1. Check that your radiator valves (TRVs) are open to allow water to flow
  2. Check the boiler pressure gauge and top up to 1.5 bar if it is low
  3. Gently bleed your radiators to remove any trapped air
  4. Press the Reset button on the boiler control panel

Parts commonly replaced

  • External System Pump
  • Safety Temperature Sensor (NTC)
  • Main Heat Exchanger (if scaled or blocked)

Related codes

Showing 91–100 of 156
D4 286

Your boiler has shut down because it thinks the water returning to the unit is dangerously hot, which usually means water isn't circulating properly.

High Engineer only £120-280

Parts commonly replaced

  • Return temperature sensor (NTC)
  • Circulation pump
  • Main heat exchanger

Related codes

D4 341

Your boiler is overheating because the water inside it is heating up much quicker than it can be pumped away.

High DIY-safe £150-350

What to check first

  1. Check that your radiator valves are fully open
  2. Ensure there is enough water pressure in the system (between 1 and 1.5 bar)
  3. Bleed any trapped air from your radiators

Parts commonly replaced

  • Circulating Pump
  • Flow Temperature Sensor (NTC)
  • Main Heat Exchanger (De-scale)

Related codes

E2

Your boiler's internal thermometer that measures the temperature of the water leaving the unit has stopped working correctly, causing the system to shut down for safety.

High Engineer only £100-£180

Parts commonly replaced

  • Central Heating Flow NTC Sensor
  • Sensor Wiring Harness

Related codes

E2 222

Your boiler has detected an electrical fault with the internal sensor that monitors the temperature of the water flowing to your radiators.

High Engineer only £120-£200

Parts commonly replaced

  • Flow Temperature Sensor (NTC thermistor)
  • Connecting wiring harness

Related codes

E2 223

Your boiler has stopped working because it has lost the connection to the internal sensor that monitors the temperature of the water leaving the unit.

High Engineer only £90-160

Parts commonly replaced

  • Flow Temperature Sensor (NTC Thermistor)
  • Wiring Harness
  • Main PCB

Related codes

E2 233

Your boiler has stopped working because it can no longer communicate with the internal sensor that monitors the temperature of the water leaving the unit.

High Engineer only £90-160

Parts commonly replaced

  • Flow temperature sensor (NTC thermistor)
  • Wiring harness
  • Main PCB

Related codes

E2 350

Your boiler has detected a fault with the sensor that monitors the water temperature leaving the unit, causing the system to shut down for safety.

High Engineer only £90-160

Parts commonly replaced

  • Flow temperature sensor (NTC thermistor)
  • Connecting wiring harness

Related codes

E2 351

Your boiler has lost its connection to the sensor that monitors the water temperature, meaning it cannot safely heat your home or water.

High Engineer only £90-160

Parts commonly replaced

  • Flow temperature sensor (NTC thermistor)
  • Wiring harness
  • Main PCB

Related codes

E5 218

Your boiler has sensed that the water inside is getting too hot and has shut down as a safety precaution.

High DIY-safe £100-280

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
  3. Reset the boiler using the reset button

Parts commonly replaced

  • Overheat Thermostat
  • NTC Temperature Sensor
  • Circulation Pump

Related codes

E9

Your boiler has shut down because it has detected that the water inside is getting too hot or the pressure is incorrect.

High DIY-safe £90-280

What to check first

  1. Check the pressure gauge on the front of the boiler is between 1 and 1.5 bar
  2. Top up the water pressure using the filling link if it is too low
  3. Ensure all radiator valves are fully open and there are no blockages
  4. Press and hold the reset button for five seconds

Parts commonly replaced

  • Overheat Thermostat
  • Temperature Sensor (NTC)
  • Circulation Pump

Related codes

Showing 101–110 of 156
E9 210

Your boiler has detected that the exhaust gases are too hot or a safety sensor has broken, causing the system to shut down for your protection.

High Engineer only £120-£280

Parts commonly replaced

  • Flue Gas NTC Sensor
  • Main Heat Exchanger
  • Overheat Thermostat

Related codes

E9 219

Your boiler has detected that it is getting too hot and has shut itself down to prevent damage to its internal parts.

High Engineer only £120-£240

Parts commonly replaced

  • Overheat thermostat
  • Temperature sensor (NTC)
  • Main heat exchanger cleaning
E9 220

Your boiler has shut down because it has detected an unsafe level of overheating or a serious fault with its primary temperature sensor.

High Engineer only £120-£280

Parts commonly replaced

  • Safety temperature sensor
  • Overheat thermostat
  • Main heat exchanger
  • Pump

Related codes

E9 224

Your boiler has switched itself off because it has detected that the internal gases have become too hot, which is a safety measure to prevent damage.

High Engineer only £120-£350

Parts commonly replaced

  • Flue gas thermostat
  • Heat exchanger (cleaning or replacement)
  • Main heat exchanger sensor

Related codes

E9 276

Your boiler has shut down because it has become too hot internally and needs to cool down for safety.

High DIY-safe £120-350

What to check first

  1. Check if your radiator valves are open to allow water to flow.
  2. Verify that your system pressure is between 1.0 and 1.5 bar on the dial.
  3. Try resetting the boiler once it has cooled down.

Parts commonly replaced

  • Central heating pump
  • Overheat thermostat
  • Main heat exchanger (flushing)
E9 277

Your boiler has shut down because it has detected internal temperatures that are too high, meaning it is overheating to protect the system.

High DIY-safe £120-£350

What to check first

  1. Check that your central heating valves are fully open.
  2. Ensure all radiator valves (TRVs) are turned to the highest setting.
  3. Check the system pressure gauge and top it up to 1.5 bar if it is too low.
  4. Reset the boiler by holding the reset button for five seconds.

Parts commonly replaced

  • Primary Heat Exchanger
  • Circulating Pump
  • Safety Temperature Limiter (Overheat Stat)

Related codes

E9 285

Your boiler has sensed that the water returning from your radiators is too hot, causing the system to shut down to prevent damage.

High DIY-safe £90-220

What to check first

  1. Check that your radiator valves are open and not turned off.
  2. Ensure there is enough water pressure in the system by checking the pressure gauge.
  3. Bleed your radiators to remove any trapped air that might be blocking water flow.

Parts commonly replaced

  • Return temperature sensor (NTC)
  • Circulation pump
  • Main heat exchanger

Related codes

E9 318

Your boiler has shut down because a safety sensor has detected that the exhaust gases are getting too hot or the sensor itself has lost its electrical connection.

High Engineer only £120-£250

Parts commonly replaced

  • Flue gas temperature sensor
  • Connection lead/wiring harness
  • Heat exchanger cleaning

Related codes

EA

Your boiler is failing to light the gas flame and has locked itself out as a safety precaution.

High DIY-safe £100-280

What to check first

  1. Check if your gas meter has credit and the isolation valve is open
  2. Check if other gas appliances in your home, like a hob, are working correctly
  3. Press the Reset button on the boiler control panel for five seconds

Parts commonly replaced

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

Related codes

EA 227

Your boiler has tried to light several times but cannot detect a stable flame, so it has shut down for safety.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances in your home, like a hob, are working to ensure gas is reaching the property.
  2. Ensure your gas emergency control valve (usually by the meter) is in the 'on' position.
  3. If it is freezing outside, check that your white plastic condensate pipe is not frozen or blocked.
  4. Press and hold the 'Reset' button for five seconds to see if the boiler restarts.

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Showing 111–120 of 156
EA 229

Your boiler has lost its flame while it was running, which means it has safely shut down because it can no longer detect the heat needed to stay on.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances in your home, like a hob, are working to confirm your gas supply is active.
  2. If it is freezing outside, check if your white plastic condensate pipe leading outdoors is frozen and thaw it with warm water.
  3. Press the 'Reset' button on the boiler control panel for five seconds to see if the system restarts.

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Spark electrode leads

Related codes

EA 234

Your boiler has lost its connection with the gas valve, meaning it cannot ignite to provide heat or hot water.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

EA 261

Your boiler has failed to ignite several times, likely due to a software or communication error within its internal control system.

High DIY-safe £180-350

What to check first

  1. Press and hold the 'Reset' button for five seconds
  2. Wait for the boiler to restart and check if the blue light remains steady
  3. If the code persists, ensure your gas supply is active at the meter

Parts commonly replaced

  • Heat Control Module (HCM)
  • Spark Electrode
  • Flame Sensing Electrode

Related codes

EA 269

Your boiler is trying to start but the internal lighting sequence is taking too long to detect a flame, causing the system to lock out for safety.

High DIY-safe £90-280

What to check first

  1. Check if your gas prepay meter has credit
  2. Check if other gas appliances in your home, like a hob, are working correctly
  3. Press the reset button on the boiler once to see if it clears the fault

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve

Related codes

EC 256

Your boiler’s internal computer has encountered a critical error and has stopped the heating process to ensure safety.

High Engineer only £280-450

Parts commonly replaced

  • Burner Control Unit
  • PCB (Printed Circuit Board)
  • Wiring Harness

Related codes

EF 349

Your boiler is slowing itself down because water isn't moving through the system quickly enough to take the heat away.

Medium DIY-safe £120-£350

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 the pump is making a humming sound or if it feels excessively hot

Parts commonly replaced

  • Circulation Pump
  • Central Heating Return Filter
  • Main Heat Exchanger (if scaled)

Related codes

EH 258

Your boiler's electronic brains have developed a fault, meaning the system cannot communicate internally and has shut down as a safety precaution.

High Engineer only £280-550

Parts commonly replaced

  • Heat Control Module (HCM)
  • PCB (Main Control Board)
  • Wiring Harness

Related codes

F0

Your boiler has experienced an internal electrical communication error, meaning it cannot process the signals needed to start up or stay running.

High Engineer only £120-£350

Parts commonly replaced

  • Wiring harness
  • Control board (PCB)
  • Ignition leads

Related codes

F0 237

Your boiler's internal computer has encountered a communication fault and can no longer control the heating or hot water safely.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

F0 238

Your boiler has detected an electrical communication problem with the internal gas control system, meaning it cannot safely light the flame to provide heating or hot water.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

Showing 121–130 of 156
F0 239

Your boiler's main internal computer has developed a fault and can no longer control the heating process safely.

High Engineer only £250-£450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Heat Control Module (HCM)

Related codes

F0 242

Your boiler’s internal computer has encountered a critical communication error and cannot tell the system to heat up.

High Engineer only £280-550

Parts commonly replaced

  • Heat Control Module (HCM)
  • Main Printed Circuit Board (PCB)

Related codes

F0 258

Your boiler’s internal computer system has detected a fatal electronic failure and can no longer control the heating process safely.

High Engineer only £250-£450

Parts commonly replaced

  • Heat Control Module (HCM)
  • Printed Circuit Board (PCB)

Related codes

F0 262

Your boiler’s internal computer brain or its memory card has developed a communication fault and can no longer control the heating process.

High Engineer only £280-550

Parts commonly replaced

  • Heat Control Module (HCM)
  • Main Printed Circuit Board (PCB)

Related codes

F0 272

Your boiler’s internal computer has encountered a critical error or is not communicating properly, meaning the system cannot run.

High Engineer only £280-550

Parts commonly replaced

  • Main PCB (Control Box)
  • HCM (Heat Control Module)

Related codes

F0 278

Your boiler's internal computer has detected a problem with its electronic sensors and cannot safely confirm the temperature.

High Engineer only £120-240

Parts commonly replaced

  • Flow temperature sensor
  • Return temperature sensor
  • Wiring harness

Related codes

F0 279

Your boiler's main internal computer has developed a serious internal fault and can no longer communicate with the parts that manage the flame.

High Engineer only £280-£550

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • KIM (Key Identification Module)

Related codes

F0 280

Your boiler's internal computer brain or its memory chip has developed a fault or is not connected properly, preventing the unit from starting.

High Engineer only £280-550

Parts commonly replaced

  • Control Box
  • Heat Control Module (HCM)

Related codes

F0 287

Your boiler's internal computer has developed a communication fault and cannot safely light the burner to provide heat.

High Engineer only £250-£450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • KIM identity module

Related codes

F0 290

Your boiler's internal computer brain is having trouble communicating or has failed, meaning the system cannot run safely.

High Engineer only £280-450

Parts commonly replaced

  • Heat Cell Module (HCM)
  • Printed Circuit Board (PCB)

Related codes

Showing 131–140 of 156
F1 259

Your boiler's computer system has detected an internal electronic failure and has shut down for safety.

High Engineer only £250-£450

Parts commonly replaced

  • Heat Control Module (HCM)
  • Main PCB (Printed Circuit Board)

Related codes

F1 263

Your boiler's internal computer brain or its memory module has developed a technical fault, preventing the system from operating.

High Engineer only £280-450

Parts commonly replaced

  • Heat Control Module (HCM)
  • Printed Circuit Board (PCB)

Related codes

F7

Your boiler thinks it can see a flame when it shouldn't be running, which is a safety precaution that prevents the unit from starting up.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation Electrode
  • Control PCB
  • Wiring Harness

Related codes

F7 228

Your boiler thinks a flame is present when there shouldn't be one, so it has locked itself out as a safety precaution.

High Engineer only £120-£350

Parts commonly replaced

  • Flame sensing electrode
  • PCB (Main circuit board)
  • Gas valve

Related codes

F7 328

Your boiler has experienced a temporary interruption in its electric power supply and needs to be reset to resume normal operation.

Low DIY-safe £0-120

What to check first

  1. Locate the reset button on the boiler control panel
  2. Press and hold the reset button for five seconds
  3. Wait for the boiler to restart and check if the fault code has cleared

Parts commonly replaced

  • None (Reset only)
  • Printed Circuit Board (PCB) if fault persists

Related codes

FA

Your boiler is still detecting a flame even though it should have turned off, which is a safety concern that requires an expert's attention.

Emergency Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Ionisation electrode
  • Control board (PCB)

Related codes

FA 306

Your boiler is still detecting a flame after it was supposed to have turned off, which is a safety conflict causing the system to lock out.

High Engineer only £120-£350

Parts commonly replaced

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

Related codes

FA 364

Your boiler has detected a potential internal gas leak or a serious safety issue within its fuel management system and has shut down to keep you safe.

Emergency Engineer only £250-£450

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

FB 365

Your boiler has detected a potential internal issue with the gas control system and has shut down for safety purposes.

Emergency Engineer only £280-450

Parts commonly replaced

  • Gas Valve
  • Ignition Lead
  • Main PCB

Related codes

FD

Your boiler thinks you have accidentally bumped the reset button and is simply waiting for you to confirm the action to restart.

Low DIY-safe

What to check first

  1. Locate the reset button on the front control panel.
  2. Press and hold the reset button for approximately 3 to 5 seconds.
  3. Wait for the display to clear the FD code and return to a normal temperature reading.
Showing 141–150 of 156
FD 231

Your boiler has lost its connection to the electrical supply or has detected an issue with the power coming into the unit.

High DIY-safe £90-280

What to check first

  1. Check if there has been a local power cut or if a fuse has tripped in your home's main consumer unit.
  2. Ensure the boiler's dedicated power switch (usually a fused spur near the boiler) is turned on.
  3. Press and hold the reset button for five seconds once power is restored.

Parts commonly replaced

  • External fuse
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

H07

Your boiler has detected that the water pressure in the system is too low, which is preventing it from providing full heating or hot water.

Medium DIY-safe £0-120

What to check first

  1. Locate the internal or external filling loop (usually a silver flexible hose with small valves).
  2. Slowly open the valves to allow water into the system while watching the pressure gauge.
  3. Close both valves tightly once the pressure needle reaches between 1 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

HrE

Your boiler is experiencing a critical electronic failure that is causing it to repeatedly restart itself, which prevents it from providing heating or hot water.

High Engineer only £280-550

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Internal Wiring Harness

Related codes

Light off

Your boiler is currently sitting in standby mode because it hasn't received a signal from your thermostat or timer to turn 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 programmer or heating clock is set to 'ON' or 'AUTO'.
  3. Replace the batteries in your wireless wall thermostat if the screen is blank.

Parts commonly replaced

  • Thermostat batteries
  • External room thermostat
  • Programmer/Timer unit
Light on

Your boiler is operating normally and is currently providing heat to your radiators or hot water tank.

Low DIY-safe

What to check first

  1. Check your thermostat settings if the house is too warm
  2. Monitor the light to ensure it turns off when the heating is turned down
  3. No action is required as this indicates normal operation
lockout

Your boiler has stopped working because it cannot detect a flame, likely due to an interruption in your gas supply.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

NO CODE 212

Your boiler is overheating because the water inside it is getting too hot too quickly, usually because it isn't moving through the system properly.

High DIY-safe £120-£350

What to check first

  1. Check that your radiator valves are open and not turned to the off position
  2. Ensure your boiler pressure is between 1 and 1.5 bar on the pressure gauge
  3. Gently bleed your radiators to remove any trapped air pockets

Parts commonly replaced

  • Central heating pump
  • Temperature thermistor (NTC sensor)
  • Main heat exchanger

Related codes

No light

Your boiler has lost power completely and the display screen is blank, meaning it cannot start the heating or hot water process.

High DIY-safe £100-£350

What to check first

  1. Check if other appliances in the house have power
  2. Ensure the boiler's fused spur switch (usually near the boiler) is turned on
  3. Check your home's main consumer unit (fuse box) to see if a circuit has tripped

Parts commonly replaced

  • Internal Glass Fuse
  • Printed Circuit Board (PCB)
  • Transformer
Primary Overheat

Your boiler has detected that the water inside the unit has become dangerously hot and has shut itself down to prevent damage or fire risk.

Emergency Engineer only £150-300

Parts commonly replaced

  • Pump
  • Plate-to-plate heat exchanger
  • NTC thermistor sensor
  • Diverter valve

Related codes

rE

Your boiler is currently going through a reset process, which usually happens after a fault has occurred or the reset button has been pressed.

Low DIY-safe £0-120

What to check first

  1. Wait for 30 seconds to see if the boiler restarts automatically
  2. Check if any other fault codes appear after the reset finishes
  3. Ensure your gas supply is active and credit is on the meter

Parts commonly replaced

  • No parts usually required for this code alone
  • Ignition Electrode
  • Printed Circuit Board (PCB)

Related codes

Showing 151–156 of 156
Sensor Fault

Your boiler is struggling to accurately measure the temperature of the water, which means it has stopped heating because it is unsure if it is safe to do so.

High Engineer only £120-200

Parts commonly replaced

  • DHW NTC sensor
  • CH NTC sensor
  • Wiring harness

Related codes

T1

Your boiler is currently running a self-diagnostic test to check if the ignition spark is working correctly.

Low DIY-safe £0-120

What to check first

  1. Wait for the test to complete automatically
  2. If the code persists, try resetting the boiler
  3. Ensure your gas supply is active

Parts commonly replaced

  • Ignition Electrode
  • Spark Lead

Related codes

T2

Your boiler is having trouble starting up because it cannot verify that the internal fan is spinning at the correct speed to safely clear exhaust fumes.

High Engineer only £180-£350

Parts commonly replaced

  • Fan Assembly
  • Air Pressure Switch
  • Main PCB

Related codes

T3

Your boiler is checking if the pump is circulating water correctly and has detected a potential blockage or pump failure.

High Engineer only £220-£450

Parts commonly replaced

  • Central heating pump
  • Printed Circuit Board (PCB)
  • Flow pipe temperature sensor

Related codes

T4

Your boiler is having trouble switching between your heating and hot water because an internal valve is stuck or failing its startup check.

High Engineer only £180-£350

Parts commonly replaced

  • Diverter valve motor
  • Diverter valve cartridge
  • Printed Circuit Board (PCB)

Related codes

T6

Your boiler's electronic control system is failing to carry out its internal safety checks, preventing the unit from starting safely.

High Engineer only £250-480

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Ionisation Electrode

Related codes