Baxi Promax Heat Fault codes & diagnostics

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

Regular Natural Gas 12-30 kW 2006-2016 Discontinued

Replaced by: Potterton Titanium Heat

This boiler uses indicator light combinations

Note which lights are on, off, or flashing and at what speed. Match the combination to the cards below. Do not reset until you have noted the pattern. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
16 High
Just want the most common Baxi Promax Heat faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 16 documented codes

Tap any card for details

LED / flash-pattern codes
Indicator Neons

Your boiler is using a combination of flashing or steady lights to signal exactly what is wrong with the system, ranging from simple pressure issues to internal component failure.

High DIY-safe £100-350

What to check first

  1. Check if the gas supply is turned on and credit is on the meter
  2. Ensure the system pressure is between 1.0 and 1.5 bar on the gauge
  3. Turn the selector switch to the reset position for five seconds and release

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Air Pressure Switch
  • Overheat Thermostat
Full explanation for Indicator Neons
Overheat indicator

Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.

High DIY-safe £80-250

What to check first

  1. Check that all your radiator valves are open to allow water to flow.
  2. Ensure your system pressure is at the correct level (usually between 1 and 1.5 bar).
  3. Press the white Reset Button on the front of the boiler.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Thermistor (NTC Sensor)
Full explanation for Overheat indicator
Digital codes
E01

Your boiler is failing to light the flame needed to heat your home, which is often caused by a temporary interruption in the gas supply or an issue with the ignition system.

High DIY-safe £100-350

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. If you have a prepayment meter, ensure you have credit and the meter is active
  3. Press the reset button or turn the control knob to 'R' for five seconds and release

Parts commonly replaced

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

Related codes

Full explanation for E01
E02

Your boiler has shut down because its internal temperature got too high, causing a safety switch to trigger and prevent damage.

High DIY-safe £100-£250

What to check first

  1. Check that your radiator valves are open and not turned off.
  2. Ensure there is no air trapped in your radiators by bleeding them.
  3. Wait for the boiler to cool down and then press the 'Reset' button.

Parts commonly replaced

  • Safety Overheat Thermostat
  • Water Pump
  • Heat Exchanger
Full explanation for E02
E03

Your boiler has detected an issue with how it clears waste gases or brings in fresh air, causing it to shut down for safety.

High Engineer only £100-£250

Parts commonly replaced

  • Air Pressure Switch
  • Venturi Tube
  • Flue Fan
Full explanation for E03
E05

Your boiler has detected a problem with the internal sensor that monitors the temperature of the water being sent to your radiators, causing the system to shut down for safety.

High Engineer only £90-160

Parts commonly replaced

  • CH Flow NTC Thermistor
  • Connecting wiring harness

Related codes

Full explanation for E05
E06

Your boiler is having trouble measuring the temperature of your hot water, which means your taps might not get warm.

High Engineer only £90-160

Parts commonly replaced

  • Domestic hot water (DHW) sensor
  • NTC thermistor
  • Wiring harness

Related codes

Full explanation for E06
E10

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

High DIY-safe £0-120

What to check first

  1. Locate the external filling loop (usually a silver braided hose with small black lever handles) under or near the boiler.
  2. Slowly open both lever valves until you hear water flowing and watch the pressure gauge.
  3. Once the gauge reaches 1.5 bar, close both valves tightly and reset the boiler.

Parts commonly replaced

  • External filling loop
  • System pressure switch
  • Expansion vessel
Full explanation for E10
E25

Your boiler has shut down because the water inside it has become too hot too quickly, usually because it isn't moving through the system properly.

High Engineer only £150-£350

Parts commonly replaced

  • Circulation Pump
  • Standard NTC Sensor
  • External Zone Valve
Full explanation for E25
E35

Your boiler thinks it sees a flame even though it hasn't finished its start-up sequence, so it has locked out as a safety precaution.

High Engineer only £100-280

Parts commonly replaced

  • Flame sensing electrode
  • PCB (Printed Circuit Board)
  • Gas valve
Full explanation for E35
Flame Failure

Your boiler has failed to light the gas flame or cannot detect that the flame is burning, causing the system to shut down for safety.

High DIY-safe £100-300

What to check first

  1. Check if your gas supply is active by testing another gas appliance like a hob.
  2. Locate the red 'Flame Failure' button on the front control panel.
  3. Press and hold the button for a few seconds to reset the boiler.

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve
Full explanation for Flame Failure
Flame Failure Reset Button

Your boiler has stopped itself from firing for safety reasons and needs a manual restart to try and light the flame again.

High DIY-safe £100-280

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. Ensure you have credit on your gas meter if applicable
  3. Press and hold the reset button for five seconds to see if the boiler restarts

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Lead
Full explanation for Flame Failure Reset Button
Overheat

Your boiler has become too hot and has switched itself off as a safety precaution.

High DIY-safe £100-350

What to check first

  1. Locate the white Reset button on the front of the boiler control panel.
  2. Press the button firmly to restart the system.
  3. Check that your radiator valves are open and that the system pressure is correct.

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • Heat Exchanger
Full explanation for Overheat
Pressure Gauge (below 0.5 bar)

Your boiler has stopped working because the water pressure is too low, often caused by a small leak or recently bled radiators.

High DIY-safe £0-120

What to check first

  1. Locate the external filling loop, which is usually a flexible silver hose with two small taps.
  2. Slowly open both taps to allow water into the system while watching the pressure gauge.
  3. Close both taps tightly once the needle reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Auto air vent
  • Expansion vessel
Full explanation for Pressure Gauge (below 0.5 bar)
Red reset button illuminated

Your boiler has failed to light the gas to start the heating process, causing it to shut down for safety.

High DIY-safe £100-350

What to check first

  1. Check that your gas emergency control valve is open and other gas appliances are working
  2. Ensure your condensate pipe has not frozen if it is a very cold day
  3. Press the red reset button once to see if the boiler restarts

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • PCB (Printed Circuit Board)
Full explanation for Red reset button illuminated
Safety Thermostat neon

Your boiler has switched itself off because it got too hot, likely due to a circulation problem or a temporary blockage in the system.

High DIY-safe £100-280

What to check first

  1. Check that your pump is running and not stuck.
  2. Ensure all radiator valves and internal stopcocks are fully open.
  3. Wait for the boiler to cool down and then turn the selector switch to 'Reset' for five seconds.
  4. Check that your system pressure is correct (usually 1.0 to 1.5 bar) if you have a sealed system.

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat (Limit Statutory)
  • Flow/Return Thermistor
Full explanation for Safety Thermostat neon