BoilerFaultCodes 1 green flash
Your boiler has reached its set temperature and is temporarily pausing its operation as normal.
Baxi 800 Fault codes & diagnostics
129 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Combi Natural Gas 25-36 kW 2019-present
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. 1 Emergency
110 High
10 Medium
8 Low
Just want the most common Baxi 800 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 129 documented codes
Tap any card for details
LED / flash-pattern codes
1 red flash Your boiler has detected that the water is either getting too hot or isn't moving through the system correctly, causing it to shut down for safety.
Your boiler has detected that the water is either getting too hot or isn't moving through the system correctly, causing it to shut down for safety.
What to check first
- Check that all radiator valves are fully open
- Check the boiler pressure gauge and top up to 1.5 bar if it is low
- Ensure the pump is not making grinding noises and bleed any air from the radiators
- Reset the boiler by turning the selector switch to 'R' for five seconds
Parts commonly replaced
- NTC Temperature Sensor
- Circulation Pump
- Plate Heat Exchanger
Related codes
2 red flashes Your boiler has become too hot and has automatically shut down as a safety precaution to prevent damage.
Your boiler has become too hot and has automatically shut down as a safety precaution to prevent damage.
What to check first
- Allow the boiler to cool down for at least 20 minutes
- Check that all radiator valves are fully open
- Press the 'R' or Reset button to try and restart the system
Parts commonly replaced
- Overheat Thermostat
- Central Heating Pump
- Thermistor
Related codes
3 green flashes Your boiler has temporarily lost its flame and is currently trying to restart itself automatically.
Your boiler has temporarily lost its flame and is currently trying to restart itself automatically.
What to check first
- Wait for the boiler to automatically attempt a restart
- Check that the gas supply is active (e.g. check other gas appliances)
- If the fault persists and changes to a solid error, try pressing the Reset button once
Parts commonly replaced
- Flame sensing electrode
- Gas valve
- Condensate trap
Related codes
3 red flashes Your boiler is failing to light its internal flame after several attempts, which means it will not be able to provide heating or hot water until it is reset or repaired.
Your boiler is failing to light its internal flame after several attempts, which means it will not be able to provide heating or hot water until it is reset or repaired.
What to check first
- Check that your gas emergency control valve is switched on and other gas appliances like your hob are working.
- Ensure your pre-paid gas meter has credit, if applicable.
- Press and hold the reset button for 5 seconds to clear the fault.
Parts commonly replaced
- Ignition electrodes
- Gas valve
- Spark generator
Related codes
4 green flashes Your boiler is temporarily struggling to talk to its internal computer and should restart itself automatically without you needing to do anything.
Your boiler is temporarily struggling to talk to its internal computer and should restart itself automatically without you needing to do anything.
What to check first
- Wait for the boiler to complete its automatic self-reset
- If the flashing continues, turn the power to the boiler off and back on at the fused spur switch
- Ensure any external room thermostats or smart controls have fresh batteries
Parts commonly replaced
- None (usually self-corrects)
- Printed Circuit Board (PCB)
Related codes
4 red flashes Your boiler's fan, which safely pushes exhaust gases out of your home, is not spinning correctly or has lost power.
Your boiler's fan, which safely pushes exhaust gases out of your home, is not spinning correctly or has lost power.
Parts commonly replaced
- Fan motor
- PCB (Main circuit board)
- Wiring harness
Related codes
5 green flashes Your boiler has experienced a brief computer glitch while loading its settings, but it is programmed to fix itself and restart automatically.
Your boiler has experienced a brief computer glitch while loading its settings, but it is programmed to fix itself and restart automatically.
What to check first
- Wait for the boiler to self-reset automatically
- If the flashing persists for more than 10 minutes, turn the selector switch to 'Reset'
- If the fault continues to return, monitor the boiler and contact a technician
Parts commonly replaced
- None (Software reset)
- Printed Circuit Board (PCB)
Related codes
5 red flashes Your boiler’s internal memory chip has developed a communication fault, meaning it cannot remember its own settings to run safely.
Your boiler’s internal memory chip has developed a communication fault, meaning it cannot remember its own settings to run safely.
Parts commonly replaced
- Parameter Storage Unit (PSU)
- Control Board (PCB)
Related codes
6 green flashes Your boiler has experienced a temporary communication hiccup and is currently trying to fix itself automatically.
Your boiler has experienced a temporary communication hiccup and is currently trying to fix itself automatically.
What to check first
- Wait for the boiler to finish its self-reset cycle
- If the flashing continues for more than 10 minutes, turn the power off and back on at the fused spur switch
- Ensure your mains water pressure hasn't dropped
Parts commonly replaced
- None (Software reset)
- Printed Circuit Board (PCB)
Related codes
Showing 11–20 of 129
6 red flashes Your boiler has encountered an internal technical error that is preventing it from running properly and needs professional attention.
Your boiler has encountered an internal technical error that is preventing it from running properly and needs professional attention.
Parts commonly replaced
- Main PCB (Printed Circuit Board)
- Wiring harness
- Gas valve
Related codes
FLASH FLASH ON Your boiler's fan, which safely pushes exhaust gases out of your home, is not spinning or starting correctly, causing the system to shut down for safety.
Your boiler's fan, which safely pushes exhaust gases out of your home, is not spinning or starting correctly, causing the system to shut down for safety.
Parts commonly replaced
- Fan assembly
- Printed Circuit Board (PCB)
- Air pressure switch
Related codes
FLASH OFF FLASH Your boiler is not receiving enough electrical power from the mains supply to operate safely.
Your boiler is not receiving enough electrical power from the mains supply to operate safely.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Mains transformer
Related codes
FLASH OFF ON Your boiler has switched itself off because it has become too hot internally, likely due to a circulation issue or a blockage.
Your boiler has switched itself off because it has become too hot internally, likely due to a circulation issue or a blockage.
What to check first
- Check that all radiator valves are fully open to allow water flow.
- Verify that your system pressure is between 1.0 and 1.5 bar on the gauge.
- Baxi 800 models often have a 'Reset' selector; turn the knob to the reset position for five seconds and release.
Parts commonly replaced
- Circulation Pump
- Overheat Thermostat
- Main Heat Exchanger (Descaling)
Related codes
FLASH ON FLASH Your boiler's internal computer has encountered a communication error and can no longer control the heating system safely.
Your boiler's internal computer has encountered a communication error and can no longer control the heating system safely.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
Related codes
FLASH ON ON Your boiler's internal computer has encountered a critical error and can no longer control the heating system safely.
Your boiler's internal computer has encountered a critical error and can no longer control the heating system safely.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Wiring Harness
Related codes
ON FLASH FLASH Your boiler is struggling to move water around the system or there is not enough water inside for it to heat up safely.
Your boiler is struggling to move water around the system or there is not enough water inside for it to heat up safely.
What to check first
- Check the pressure gauge and top it up to 1.5 bar using the filling loop if it is too low
- Ensure all radiator valves and isolation valves under the boiler are fully open
- Bleed your radiators to remove any trapped air pockets
- Reset the boiler once the pressure is corrected
Parts commonly replaced
- Circulation Pump
- Primary Heat Exchanger
- Flow/Return Thermistors
Related codes
ON FLASH ON Your boiler's temperature sensors have developed a fault, meaning the system can no longer safely monitor how hot the water is getting.
Your boiler's temperature sensors have developed a fault, meaning the system can no longer safely monitor how hot the water is getting.
Parts commonly replaced
- NTC Thermistor (Flow or Return)
- Wiring Harness
Related codes
ON OFF FLASH Your boiler has detected that the electrical wiring coming into the unit from your house has been connected the wrong way around.
Your boiler has detected that the electrical wiring coming into the unit from your house has been connected the wrong way around.
Parts commonly replaced
- External wiring connections
- Fused spur
- Printed Circuit Board (PCB) if damaged by reverse polarity
Related codes
ON ON FLASH Your boiler's internal computer has encountered a critical error and can no longer control the heating system safely.
Your boiler's internal computer has encountered a critical error and can no longer control the heating system safely.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Wiring Harness
Related codes
Digital codes
110 Your boiler has reached an unsafe temperature and has automatically shut down to prevent damage.
Your boiler has reached an unsafe temperature and has automatically shut down to prevent damage.
What to check first
- Turn the boiler off and allow it to cool down for 20 minutes.
- Check that all radiator valves are fully open.
- Bleed your radiators using a radiator key to release trapped air.
- Check the boiler pressure gauge and top it up to 1.5 bar if it has dropped.
- Reset the boiler.
Parts commonly replaced
- Overheat Thermostat
- Circulation Pump
- NTC Temperature Sensor
Related codes
117 Your boiler has too much water in the system, which puts extra stress on the internal components and may cause it to stop working for safety.
Your boiler has too much water in the system, which puts extra stress on the internal components and may cause it to stop working for safety.
What to check first
- Check that the internal or external filling loop valves are fully closed.
- Locate a radiator bleed valve and use a key to release water into a container to lower the pressure.
- Monitor the pressure gauge until it returns to between 1.0 and 1.5 bar.
- Reset the boiler once the pressure has been reduced.
Parts commonly replaced
- Expansion Vessel
- Filling Loop Valve
- Pressure Relief Valve
Related codes
118 Your boiler has stopped working because the water pressure inside the system has dropped below the minimum level required to run safely.
Your boiler has stopped working because the water pressure inside the system has dropped below the minimum level required to run safely.
What to check first
- Locate the filling loop (the flexible silver hose) underneath the boiler.
- Slowly open the one or two small taps on the filling loop until you hear water moving.
- Watch the pressure gauge and close the taps firmly once it reaches between 1 and 1.5 bar.
Parts commonly replaced
- Filling loop
- Expansion vessel
- Pressure relief valve
Related codes
119 Your boiler has stopped working because the water pressure in the system has dropped too low to operate safely.
Your boiler has stopped working because the water pressure in the system has dropped too low to operate safely.
What to check first
- Locate the filling loop (the flexible braided hose) underneath your boiler or on the nearby pipework.
- Slowly open the one or two taps/levers on the filling loop to allow water into the system.
- Watch the pressure gauge and close the taps once the needle reaches between 1 and 1.5 bar, then restart your boiler.
Parts commonly replaced
- Filling loop
- Expansion vessel
- Pressure relief valve
Related codes
125 Your boiler has sensed that water is not moving through the system correctly, which is usually caused by trapped air or a blockage.
Your boiler has sensed that water is not moving through the system correctly, which is usually caused by trapped air or a blockage.
What to check first
- Check that your system pressure is between 1 and 1.5 bar on the gauge
- Bleed all radiators to remove any trapped air
- Ensure all radiator valves and the boiler's isolation valves are fully open
Parts commonly replaced
- Circulation pump
- Water pressure sensor
- Automatic air vent
Related codes
127 Your boiler has failed to heat the water to a high enough temperature to kill off any potentially harmful bacteria in the system.
Your boiler has failed to heat the water to a high enough temperature to kill off any potentially harmful bacteria in the system.
What to check first
- Check that your hot water cylinder thermostat is set to at least 60°C
- Ensure your heating and hot water timers allow enough time for the tank to reach full temperature
- Reset the boiler to see if the cycle completes successfully on the next attempt
Parts commonly replaced
- Cylinder thermostat
- NTC thermistor (sensor)
- Diverter valve
Related codes
128 Your boiler started to heat up but the flame went out unexpectedly while it was running.
Your boiler started to heat up but the flame went out unexpectedly while it was running.
What to check first
- Check that your gas emergency control valve is open and you have credit on your gas meter
- Press and hold the 'R' or Reset button for five seconds
- Check if other gas appliances in your home, like a hob, are working correctly to rule out a gas supply issue
Parts commonly replaced
- Flame sensing electrode
- Gas valve
- Ignition lead
Related codes
133 Your boiler has failed to light after several attempts, meaning it cannot produce heat or hot water.
Your boiler has failed to light after several attempts, meaning it cannot produce heat or hot water.
What to check first
- Check that your gas meter has credit and the isolation valve is open
- Press and hold the 'R' or Reset button for five seconds
- Ensure the condensate pipe (the white plastic pipe outside) isn't frozen if it is cold weather
Parts commonly replaced
- Ignition electrode
- Flame sensing probe
- Gas valve
- PCB
Related codes
153 Your boiler has been manually reset too many times in a short period and has temporarily locked itself for safety.
Your boiler has been manually reset too many times in a short period and has temporarily locked itself for safety.
What to check first
- Locate the selector knob on the front of the boiler.
- Turn the knob to the 'R' (Reset) position and hold it for at least 5 seconds.
- Wait for the boiler to complete its restart sequence and see if the code clears.
Parts commonly replaced
- None (Software Lock)
- Printed Circuit Board (PCB)
Related codes
160 Your boiler's fan is not spinning at the correct speed, which means it cannot safely clear away waste gases to allow the boiler to start.
Your boiler's fan is not spinning at the correct speed, which means it cannot safely clear away waste gases to allow the boiler to start.
Parts commonly replaced
- Fan assembly
- Printed Circuit Board (PCB)
- Wiring harness
Related codes
Showing 31–40 of 129
162 Your boiler has detected an issue with how air is moving through the system, meaning it cannot safely clear away waste gases and has shut down as a precaution.
Your boiler has detected an issue with how air is moving through the system, meaning it cannot safely clear away waste gases and has shut down as a precaution.
Parts commonly replaced
- Air Pressure Switch
- Venturi Tube
- Fan
Related codes
164 Your boiler has detected an issue with the sensor that monitors water pressure or flow, preventing it from heating your home safely.
Your boiler has detected an issue with the sensor that monitors water pressure or flow, preventing it from heating your home safely.
What to check first
- Check if your boiler pressure gauge is between 1.0 and 1.5 bar
- If pressure is too low, use the filling loop to top it up
- Reset the boiler by turning the selector knob to 'R' for five seconds
Parts commonly replaced
- Water pressure sensor
- Flow switch
- Wiring harness
Related codes
166 Your boiler has detected a problem with how air and waste gases are moving through the system, preventing it from firing up for your safety.
Your boiler has detected a problem with how air and waste gases are moving through the system, preventing it from firing up for your safety.
Parts commonly replaced
- Air Pressure Switch
- Venturi Tube
- Fan Assembly
Related codes
270 Your boiler has sensed a rapid rise in temperature because there is not enough water moving through the system to absorb the heat.
Your boiler has sensed a rapid rise in temperature because there is not enough water moving through the system to absorb the heat.
What to check first
- Check the pressure gauge and top up to between 1.0 and 1.5 bar if it is too low
- Ensure all radiator valves are open and not turned off
- Restart the boiler using the reset button
Parts commonly replaced
- Circulation pump
- Main heat exchanger
- Overheat thermostat
Related codes
432 Your boiler has lost its electrical safety grounding connection, which prevents it from running for safety reasons.
Your boiler has lost its electrical safety grounding connection, which prevents it from running for safety reasons.
Parts commonly replaced
- Main PCB
- Wiring Harness
- Earth Bonding Cable
Related codes
433 Your boiler has switched itself off because it has become too hot inside, likely due to water not circulating properly.
Your boiler has switched itself off because it has become too hot inside, likely due to water not circulating properly.
What to check first
- Check that your radiator valves are fully open
- Ensure your system pressure is between 1.0 and 1.5 bar on the gauge
- Bleed your radiators to remove any trapped air
Parts commonly replaced
- Circulation Pump
- Temperature Sensor (NTC Thermistor)
- Main Heat Exchanger (Descaling)
Related codes
E.00 – .04 Your boiler has detected a fault with the sensor that monitors water returning from your radiators, meaning it cannot safely regulate the temperature and has stopped working.
Your boiler has detected a fault with the sensor that monitors water returning from your radiators, meaning it cannot safely regulate the temperature and has stopped working.
Parts commonly replaced
- Return temperature sensor (NTC thermistor)
- Sensor wiring harness
E.00 – .05 Your boiler has stopped working because it cannot correctly detect the temperature of the water returning to the unit.
Your boiler has stopped working because it cannot correctly detect the temperature of the water returning to the unit.
Parts commonly replaced
- Return temperature sensor (NTC thermistor)
- Wiring harness connecting the sensor
Related codes
E.01 – .02 Your boiler has detected that the water coming back from your radiators is hotter than the water going out, which usually means the water isn't flowing correctly or a sensor is misreading.
Your boiler has detected that the water coming back from your radiators is hotter than the water going out, which usually means the water isn't flowing correctly or a sensor is misreading.
What to check first
- Check that all radiator valves (TRVs) are fully open
- Ensure the boiler pressure is between 1.0 and 1.5 bar on the gauge
- Gently bleed your radiators to remove any trapped air
- Reset the boiler by turning the selector switch to 'R' for five seconds
Parts commonly replaced
- Flow/Return NTC thermistor
- Circulation pump
- Internal pipework (de-scaling)
E.01 – .04 Your boiler is struggling to keep its flame lit and has shut down as a safety precaution after multiple failed attempts.
Your boiler is struggling to keep its flame lit and has shut down as a safety precaution after multiple failed attempts.
What to check first
- Check that your gas supply is turned on at the meter
- If you have a prepay meter, ensure you have sufficient credit
- Press and hold the reset button for five seconds
Parts commonly replaced
- Ignition electrode
- Flame sensing probe
- Gas valve
- PCB
Related codes
Showing 41–50 of 129
E.01 – .11 Your boiler has detected that the fan is spinning at the wrong speed, likely due to a strong gust of wind outside or a fault with the air supply system.
Your boiler has detected that the fan is spinning at the wrong speed, likely due to a strong gust of wind outside or a fault with the air supply system.
What to check first
- Press and hold the 'R' or 'Reset' button for five seconds
- Check the external flue pipe on your outside wall for any obstructions like leaves or debris
- If it is a very windy day, wait for the weather to calm down and try resetting the boiler again
Parts commonly replaced
- Fan
- Air Pressure Switch
- PCB (Printed Circuit Board)
Related codes
E.01 – .12 Your boiler has sensed that the water returning from the radiators is hotter than the water leaving the boiler, which suggests a circulation or sensor error that needs a manual reset.
Your boiler has sensed that the water returning from the radiators is hotter than the water leaving the boiler, which suggests a circulation or sensor error that needs a manual reset.
What to check first
- Locate the reset button or turn the selector knob to 'R' for 5 seconds.
- Release the button and wait for the boiler to attempt to restart.
- Check that your radiator valves are open to ensure water can flow properly.
Parts commonly replaced
- Return NTC thermistor
- Flow NTC thermistor
- Pump
E.01 – .17 Your boiler has stopped working because water isn't moving through the system correctly, which could be due to a trapped air bubble or a faulty connection.
Your boiler has stopped working because water isn't moving through the system correctly, which could be due to a trapped air bubble or a faulty connection.
What to check first
- Press and hold the 'R' (Reset) button for five seconds
- Check that your radiator valves are open
- Ensure your boiler pressure is between 1.0 and 1.5 bar on the gauge
Parts commonly replaced
- Circulation Pump
- NTC Temperature Sensor
- Wiring Loom
Related codes
E.01 – .20 Your boiler has shut down because it is getting too hot inside, likely due to water not moving through the system properly or a sensor fault.
Your boiler has shut down because it is getting too hot inside, likely due to water not moving through the system properly or a sensor fault.
Parts commonly replaced
- Flue gas NTC sensor
- Main heat exchanger
- Circulation pump
E.02 – .00 Your boiler is simply letting you know that the reset button has been held down or activated.
Your boiler is simply letting you know that the reset button has been held down or activated.
What to check first
- Wait up to 30 seconds for the boiler to complete its internal checks.
- The code should clear automatically and return to the normal temperature display.
- If the code persists, try pressing the reset button once more briefly.
E.02 – .07 Your boiler has stopped working because the water pressure in the system has dropped too low to operate safely.
Your boiler has stopped working because the water pressure in the system has dropped too low to operate safely.
What to check first
- Locate the filling loop (usually two blue levers or a braided hose) underneath the boiler.
- Slowly open both taps until you hear water entering the system and watch the pressure gauge.
- Close both taps tightly once the pressure gauge reaches between 1.0 and 1.5 bar.
Parts commonly replaced
- Filling loop
- Expansion vessel
- Pressure relief valve
Related codes
E.02 – .16 Your boiler's internal computer has encountered a critical communication error or hardware failure and can no longer control the heating process.
Your boiler's internal computer has encountered a critical communication error or hardware failure and can no longer control the heating process.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Channel Service Unit
E.02 – .17 Your boiler's main control centre is unable to talk to the part that manages the gas supply, meaning the system cannot safely light itself.
Your boiler's main control centre is unable to talk to the part that manages the gas supply, meaning the system cannot safely light itself.
Parts commonly replaced
- Gas Valve
- Printed Circuit Board (PCB)
- Wiring Harness
E.02 – .19 Your boiler's internal configuration settings have been altered or are mismatched, which is preventing it from running correctly.
Your boiler's internal configuration settings have been altered or are mismatched, which is preventing it from running correctly.
Parts commonly replaced
- Jumper Link
- Printed Circuit Board (PCB)
E.02 – .20 Your boiler's internal computer settings have been adjusted incorrectly, meaning the control board doesn't recognize how the unit is supposed to operate.
Your boiler's internal computer settings have been adjusted incorrectly, meaning the control board doesn't recognize how the unit is supposed to operate.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Jumper Link
Related codes
Showing 51–60 of 129
E.02 – .21 Your boiler's internal configuration settings have been altered or are mismatched, which means the control board isn't sure how to operate correctly.
Your boiler's internal configuration settings have been altered or are mismatched, which means the control board isn't sure how to operate correctly.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Configuration Jumper/Selector
E.02 – .47 Your boiler is having trouble communicating with your external thermostat or heating controls due to a wiring issue.
Your boiler is having trouble communicating with your external thermostat or heating controls due to a wiring issue.
Parts commonly replaced
- Control wiring
- External thermostat
- Receiver unit
Related codes
E.02 – .48 Your boiler is having trouble communicating with your thermostat or smart home hub, meaning it cannot receive the command to turn on the heating.
Your boiler is having trouble communicating with your thermostat or smart home hub, meaning it cannot receive the command to turn on the heating.
What to check first
- Check batteries in your wall-mounted thermostat and replace if necessary.
- Ensure your internet router and smart home hub are switched on and connected.
- Try to re-pair the thermostat with the boiler following the manufacturer's pairing instructions.
- Reset the boiler by turning the selector knob to 'R' for five seconds.
Parts commonly replaced
- Wireless Receiver
- Smart Thermostat
- RF Communication Module
E.04 – .00 Your boiler has lost communication with the internal gas control system, meaning it cannot safely ignite to provide heat or hot water.
Your boiler has lost communication with the internal gas control system, meaning it cannot safely ignite to provide heat or hot water.
Parts commonly replaced
- Gas Valve
- Printed Circuit Board (PCB)
- Wiring Harness
Related codes
E.04 – .01 Your boiler has stopped working because it cannot correctly measure the temperature of the water leaving the unit due to a faulty or loose electrical sensor.
Your boiler has stopped working because it cannot correctly measure the temperature of the water leaving the unit due to a faulty or loose electrical sensor.
Parts commonly replaced
- Flow Temperature Sensor (NTC Thermistor)
- Wiring Harness
E.04 – .02 Your boiler has stopped working because it can no longer accurately measure the temperature of the water leaving the unit.
Your boiler has stopped working because it can no longer accurately measure the temperature of the water leaving the unit.
Parts commonly replaced
- Flow Temperature Sensor (NTC Thermistor)
- Wiring Harness
E.04 – .03 Your boiler has shut down because it is overheating, which usually means the water isn't moving through the system properly.
Your boiler has shut down because it is overheating, which usually means the water isn't moving through the system properly.
What to check first
- Check that your radiator valves are open and not turned to the off position.
- Ensure your boiler pressure is between 1.0 and 1.5 bar on the gauge.
- Restart the boiler by holding the reset button for five seconds.
Parts commonly replaced
- Circulating Pump
- Main Heat Exchanger
- Flow and Return Thermistors
Related codes
E.04 – .04 Your boiler has detected a problem with the sensor that monitors exhaust gases, causing it to shut down for safety.
Your boiler has detected a problem with the sensor that monitors exhaust gases, causing it to shut down for safety.
Parts commonly replaced
- Flue temperature sensor (NTC)
- Wiring harness
- Printed Circuit Board (PCB)
E.04 – .05 Your boiler has detected an issue with the sensor that monitors the temperature of the exhaust fumes, causing the system to shut down for safety.
Your boiler has detected an issue with the sensor that monitors the temperature of the exhaust fumes, causing the system to shut down for safety.
Parts commonly replaced
- Flue Temperature Sensor (NTC)
- Wiring harness
- Main PCB
E.04 – .06 Your boiler has shut down because it is getting too hot internally, often due to a lack of water flow or a blocked flue.
Your boiler has shut down because it is getting too hot internally, often due to a lack of water flow or a blocked flue.
Parts commonly replaced
- Flue Thermistor
- Heat Exchanger
- Circulation Pump
Related codes
Showing 61–70 of 129
E.04 – .08 Your boiler has detected that it is getting too hot and has shut itself down to prevent damage, often caused by water not moving through the system correctly.
Your boiler has detected that it is getting too hot and has shut itself down to prevent damage, often caused by water not moving through the system correctly.
What to check first
- Check that all radiator valves are fully open
- Check the boiler pressure gauge and top up to 1.5 bar if it is low
- Reset the boiler by turning the selector knob to 'R' for five seconds
Parts commonly replaced
- Circulation Pump
- Overheat Thermostat
- NTC Temperature Sensor
Related codes
E.04 – .10 Your boiler is trying to start up but cannot light the flame, which is why your heating and hot water have stopped working.
Your boiler is trying to start up but cannot light the flame, which is why your heating and hot water have stopped working.
What to check first
- Check if other gas appliances, like a cooker hob, are working to confirm your gas supply is active.
- If you have a prepay meter, check that you have enough credit.
- Press and hold the Reset button for five seconds to see if the boiler restarts.
Parts commonly replaced
- Ignition electrode
- Gas valve
- Spark generator
Related codes
E.04 – .12 Your boiler thinks a flame is present even when it should be off, or it is struggling to regulate the gas and air mixture correctly.
Your boiler thinks a flame is present even when it should be off, or it is struggling to regulate the gas and air mixture correctly.
Parts commonly replaced
- Ionisation probe
- Gas valve
- PCB
- Electrode
Related codes
E.04 – .13 Your boiler has detected a serious problem with the fan that safely removes exhaust gases, meaning the system has shut down for safety.
Your boiler has detected a serious problem with the fan that safely removes exhaust gases, meaning the system has shut down for safety.
Parts commonly replaced
- Fan assembly
- Fan wiring harness
- Printed Circuit Board (PCB)
Related codes
E.04 – .17 Your boiler has detected a serious issue with the gas flow or the internal combustion system and has locked itself out for safety.
Your boiler has detected a serious issue with the gas flow or the internal combustion system and has locked itself out for safety.
Parts commonly replaced
- Gas valve
- Printed Circuit Board (PCB)
- Fan and venturi assembly
E0 Your boiler's internal thermometer has stopped working correctly, meaning the system cannot safely monitor the water temperature to heat your home.
Your boiler's internal thermometer has stopped working correctly, meaning the system cannot safely monitor the water temperature to heat your home.
Parts commonly replaced
- NTC Temperature Sensor
- Wiring Harness Connection
Related codes
E1 Your boiler has become too hot and has shut down as a safety precaution to prevent damage.
Your boiler has become too hot and has shut down as a safety precaution to prevent damage.
What to check first
- Turn off the boiler and allow it to cool down completely.
- Bleed all radiators using a radiator key to release trapped air.
- Check the boiler pressure gauge and top it up to 1.5 bar if it has dropped.
- Reset the boiler by turning the selector switch to 'R' for five seconds.
Parts commonly replaced
- Overheat Thermostat
- Central Heating Pump
- Heat Exchanger (Descaling)
Related codes
E2 Your boiler is struggling to move water through the system, which is usually caused by trapped air or a blockage in your pipes or radiators.
Your boiler is struggling to move water through the system, which is usually caused by trapped air or a blockage in your pipes or radiators.
What to check first
- Turn off your heating and let the radiators cool down completely.
- Use a radiator key to bleed all radiators, starting with the one furthest from the boiler.
- Check your boiler pressure gauge and top it up to between 1 and 1.5 bar if it has dropped.
- Restart the boiler to see if the fault code has cleared.
Parts commonly replaced
- Circulation pump
- Central heating filter
- Automatic air vent
Related codes
E3 Your boiler's computer has developed a fault and is unable to communicate with its internal parts, meaning the system cannot run safely.
Your boiler's computer has developed a fault and is unable to communicate with its internal parts, meaning the system cannot run safely.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Wiring Harness
Related codes
E4 Your boiler has failed to ignite and heat up, which is often caused by trapped air in the system or a temporary interruption to your gas supply.
Your boiler has failed to ignite and heat up, which is often caused by trapped air in the system or a temporary interruption to your gas supply.
What to check first
- Check that your gas supply is active and credit is on the meter
- Press and hold the 'Reset' button for five seconds
- Turn off the heating and use a radiator key to bleed air from all radiators
- Check the boiler pressure gauge and top up to 1.5 bar if it has dropped
Parts commonly replaced
- Ignition electrode
- Gas valve
- Flame sensor
Related codes
Showing 71–80 of 129
E09 Your boiler has detected a communication problem with its gas control system and has shut down as a safety precaution.
Your boiler has detected a communication problem with its gas control system and has shut down as a safety precaution.
Parts commonly replaced
- Gas valve wiring harness
- Gas Valve
- Printed Circuit Board (PCB)
E10 Your boiler has lost communication with the sensor outside that helps it adjust to the weather, but it should still provide heating and hot water as normal.
Your boiler has lost communication with the sensor outside that helps it adjust to the weather, but it should still provide heating and hot water as normal.
Parts commonly replaced
- Outdoor weather compensation sensor
- Sensor wiring
Related codes
E12 Your boiler has detected that water is not circulating correctly through the system, preventing it from heating up safely.
Your boiler has detected that water is not circulating correctly through the system, preventing it from heating up safely.
What to check first
- Check that the central heating valves under the boiler are fully open
- Ensure all radiator valves (TRVs) are turned to the highest setting
- Check the boiler pressure gauge and top up to 1.5 bar if it is low
- Restart the boiler by holding the reset button for five seconds
Parts commonly replaced
- Pump
- Flow Sensor
- Main Heat Exchanger (Cleaning)
Related codes
E13 Your boiler has detected that a internal water valve is stuck in the 'on' position even though the pump has stopped, causing the system to shut down for safety.
Your boiler has detected that a internal water valve is stuck in the 'on' position even though the pump has stopped, causing the system to shut down for safety.
Parts commonly replaced
- Differential pressure switch
- Hydraulic microswitch
- Clogged bypass
Related codes
E15 Your boiler has detected an internal electrical communication error between the main control board and the part that manages the gas flow, causing the system to shut down for safety.
Your boiler has detected an internal electrical communication error between the main control board and the part that manages the gas flow, causing the system to shut down for safety.
Parts commonly replaced
- Gas Valve
- Printed Circuit Board (PCB)
- Wiring Harness
Related codes
E20 Your boiler's temperature sensor has developed a fault, meaning the system cannot accurately measure how hot the water is for your radiators.
Your boiler's temperature sensor has developed a fault, meaning the system cannot accurately measure how hot the water is for your radiators.
Parts commonly replaced
- Central Heating (CH) NTC Thermistor
- Connecting wiring harness
Related codes
E28 Your boiler has detected a problem with how it disposes of waste gases or a blockage in its drainage system, causing it to shut down for safety.
Your boiler has detected a problem with how it disposes of waste gases or a blockage in its drainage system, causing it to shut down for safety.
What to check first
- Check the external condensate pipe for signs of freezing if the weather is very cold
- Thaw any frozen external pipes using warm (not boiling) water
- Check the flue terminal on the outside of your house for any obvious obstructions like debris or bird nests
- Press the Reset button for five seconds
Parts commonly replaced
- Flue NTC Sensor
- Air Pressure Switch
- Condensate Trap
Related codes
E40 Your boiler has detected an issue with the sensor that monitors the temperature of the water returning from your radiators.
Your boiler has detected an issue with the sensor that monitors the temperature of the water returning from your radiators.
Parts commonly replaced
- Central heating return NTC thermistor
- Wiring harness
Related codes
E50 Your boiler's hot water sensor has developed a fault, meaning it cannot accurately measure the temperature of the water coming out of your taps.
Your boiler's hot water sensor has developed a fault, meaning it cannot accurately measure the temperature of the water coming out of your taps.
Parts commonly replaced
- Hot water NTC thermistor
- Wiring harness
Related codes
E53 Your boiler is not getting enough air to burn gas safely, which often means the exhaust pipe outside is obstructed or there is an issue with the internal sensors.
Your boiler is not getting enough air to burn gas safely, which often means the exhaust pipe outside is obstructed or there is an issue with the internal sensors.
What to check first
- Locate your boiler's flue pipe on the outside wall of your home.
- Check for and remove any external blockages such as debris, leaves, bird nests, or thick ice.
- Restart the boiler using the reset button once the flue is clear.
Parts commonly replaced
- Flue terminal or seals
- Gas valve
- Electrode assembly
Related codes
Showing 81–90 of 129
E54 Your boiler is struggling to detect when you turn on a hot tap, meaning you might have inconsistent or no hot water.
Your boiler is struggling to detect when you turn on a hot tap, meaning you might have inconsistent or no hot water.
Parts commonly replaced
- DHW Flow Sensor
- Wiring Harness
E55 Your boiler's electronic brain needs to recalibrate its combustion settings to ensure it is burning gas safely and efficiently.
Your boiler's electronic brain needs to recalibrate its combustion settings to ensure it is burning gas safely and efficiently.
What to check first
- Press and hold the 'R' or Reset button for at least 5 seconds
- Wait for the boiler to complete its automatic recalibration sequence
- If the code persists, check that your gas supply is active (e.g., check other gas appliances)
Parts commonly replaced
- Gas Valve
- Electrode
- PCB (Printed Circuit Board)
Related codes
E78 Your boiler has detected an issue with the sensor that monitors internal water pressure, causing the system to stop working for safety.
Your boiler has detected an issue with the sensor that monitors internal water pressure, causing the system to stop working for safety.
Parts commonly replaced
- Water pressure sensor
- Sensor wiring harness
Related codes
E83/E84/E85/E86/E87 Your boiler's main control board has lost contact with its internal components or the external thermostat, preventing it from functioning.
Your boiler's main control board has lost contact with its internal components or the external thermostat, preventing it from functioning.
What to check first
- Check that your smart thermostat bridge or hub is plugged in and has power
- Replace the batteries in your room thermostat or programmer
- Turn the boiler off at the fused spur switch, wait 30 seconds, and turn it back on to reset the connection
Parts commonly replaced
- Printed Circuit Board (PCB)
- Wiring Loom
- External Thermostat/Programmer
E92 Your boiler has detected an issue with the air and gas mixture while trying to automatically tune itself for efficient burning.
Your boiler has detected an issue with the air and gas mixture while trying to automatically tune itself for efficient burning.
Parts commonly replaced
- Gas valve
- Electrode
- PCB
Related codes
E100 Your boiler's computer brain has lost its internal time setting, often due to a temporary glitch or a failing internal component.
Your boiler's computer brain has lost its internal time setting, often due to a temporary glitch or a failing internal component.
What to check first
- Turn the boiler off at the main power switch for 30 seconds and turn it back on.
- Press and hold the 'Reset' button for five seconds.
- If the code persists, try to manually set the time using the boiler's control panel menu.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Display Interface Module
Related codes
E109 Your boiler is overheating because the water isn't moving around the system properly, causing the safety sensors to shut the unit down.
Your boiler is overheating because the water isn't moving around the system properly, causing the safety sensors to shut the unit down.
What to check first
- Check that your boiler pressure is between 1 and 1.5 bar on the gauge.
- Ensure all radiator valves and the isolation valves under the boiler are fully open.
- Gently bleed your radiators to remove any trapped air pockets.
Parts commonly replaced
- Circulation Pump
- Main Heat Exchanger (Cleaning/Descaling)
- Pump Lead
Related codes
E110 Your boiler has likely overheated, causing a safety sensor to automatically shut the system down to prevent damage.
Your boiler has likely overheated, causing a safety sensor to automatically shut the system down to prevent damage.
What to check first
- Check that your radiator valves are open and not turned off.
- Ensure your system pressure is topped up to between 1 and 1.5 bar.
- Allow the boiler to cool down for 30 minutes and then press the 'Reset' button.
Parts commonly replaced
- Overheat Thermostat
- Circulation Pump
- Temperature Sensor (NTC)
Related codes
E117 Your boiler has detected that there is too much water pressure in the system, which causes the unit to shut down for safety.
Your boiler has detected that there is too much water pressure in the system, which causes the unit to shut down for safety.
What to check first
- Locate a radiator bleed valve and a radiator key.
- With the heating off, slowly open the valve into a cloth or bowl to release water and lower the pressure.
- Monitor the boiler pressure gauge until it returns to the normal green zone (typically 1.0 to 1.5 bar).
Parts commonly replaced
- Filling loop valve
- Expansion vessel
- Pressure relief valve
Related codes
E118 Your boiler has stopped working because the water pressure in the system has dropped too low and needs to be topped up.
Your boiler has stopped working because the water pressure in the system has dropped too low and needs to be topped up.
What to check first
- Locate the filling loop (the flexible silver hose) underneath your boiler.
- Slowly open both blue tap handles until you hear water flowing.
- Watch the pressure gauge and close both taps tightly once the needle reaches between 1 and 1.5 bar.
Parts commonly replaced
- Filling loop
- Expansion vessel
- Pressure sensor
Related codes
Showing 91–100 of 129
E119 Your boiler has stopped working because the water pressure is too low for it to operate safely.
Your boiler has stopped working because the water pressure is too low for it to operate safely.
What to check first
- Locate the filling loop (usually blue levers or a braided hose under the boiler)
- Slowly open the valves until you hear water flowing and the gauge reaches between 1 and 1.5 bar
- Close both valves fully and press the 'R' or 'Reset' button on the boiler
Parts commonly replaced
- Water pressure sensor
- Filling loop
- Expansion vessel
Related codes
E125 Your boiler has detected that water is not circulating correctly around the system, which is usually caused by an air lock or a pump failure.
Your boiler has detected that water is not circulating correctly around the system, which is usually caused by an air lock or a pump failure.
What to check first
- Ensure all radiator valves are fully open
- Bleed all radiators to remove trapped air
- Check that the boiler pressure is between 1 and 1.5 bar on the gauge
- Try resetting the boiler using the reset button
Parts commonly replaced
- Circulating Pump
- Automatic Air Vent
- Diverter Valve
Related codes
E128 Your boiler is struggling to keep its internal flame lit and has shut down as a safety precaution after several unsuccessful attempts.
Your boiler is struggling to keep its internal flame lit and has shut down as a safety precaution after several unsuccessful attempts.
What to check first
- Check that your gas supply is turned on at the meter
- Check if any other gas appliances in your home are working
- Reset the boiler by turning the selector knob to 'R' for five seconds
Parts commonly replaced
- Flame sensing electrode
- Ignition lead
- Gas valve
Related codes
E129 Your boiler is struggling to maintain a steady flame during its automatic setup process, causing it to shut down for safety.
Your boiler is struggling to maintain a steady flame during its automatic setup process, causing it to shut down for safety.
Parts commonly replaced
- Ignition electrode
- Flame sensing cable
- Gas valve
- PCB
Related codes
E130 Your boiler has shut down because a sensor has detected that the exhaust gases are getting too hot, or the sensor itself has developed a fault.
Your boiler has shut down because a sensor has detected that the exhaust gases are getting too hot, or the sensor itself has developed a fault.
Parts commonly replaced
- Flue NTC Sensor
- Heat Exchanger (Cleaning/Descaling)
- Wiring Harness
Related codes
E131 Your boiler has switched itself off for safety because the exhaust gases have reached a temperature that is too high.
Your boiler has switched itself off for safety because the exhaust gases have reached a temperature that is too high.
Parts commonly replaced
- Main Heat Exchanger
- Flue Thermostat
- Temperature Sensor (NTC)
Related codes
E133 Your boiler has failed to light because it either isn't receiving gas or the system cannot detect a flame.
Your boiler has failed to light because it either isn't receiving gas or the system cannot detect a flame.
What to check first
- Check that your gas emergency control valve is open and any prepay meter has credit
- Press and hold the 'R' or Reset button for 5 seconds
- In freezing temperatures, check if the white plastic condensate pipe outside is frozen and thaw with warm water
Parts commonly replaced
- Gas Valve
- Ignition Electrode
- Printed Circuit Board (PCB)
Related codes
E134 Your boiler has tried to ignite several times but cannot detect a flame, likely because gas isn't reaching the burner or the ignition system has failed.
Your boiler has tried to ignite several times but cannot detect a flame, likely because gas isn't reaching the burner or the ignition system has failed.
What to check first
- Check that your gas emergency control valve is open and you have credit on your gas meter.
- Try resetting the boiler by turning the selector knob to 'R' and holding it for at least five seconds.
- Check if other gas appliances in your home, such as a hob, are working correctly to rule out a wider gas supply issue.
Parts commonly replaced
- Gas Valve
- Ignition Electrode
- Spark Generator
- Printed Circuit Board (PCB)
Related codes
E135 Your boiler has lost its connection to the gas supply due to an internal electronic communication failure, meaning it cannot ignite to provide heat or hot water.
Your boiler has lost its connection to the gas supply due to an internal electronic communication failure, meaning it cannot ignite to provide heat or hot water.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Gas Valve
- Wiring Harness
Related codes
E154 Your boiler has detected that water is not circulating correctly or the temperature sensors are giving conflicting readings.
Your boiler has detected that water is not circulating correctly or the temperature sensors are giving conflicting readings.
Parts commonly replaced
- Flow temperature sensor
- Return temperature sensor
- Circulation pump
Related codes
Showing 101–110 of 129
E160 Your boiler's fan, which safely pushes exhaust fumes out of the house, has stopped working correctly and needs expert attention.
Your boiler's fan, which safely pushes exhaust fumes out of the house, has stopped working correctly and needs expert attention.
Parts commonly replaced
- Fan assembly
- Fan wiring harness
- Printed Circuit Board (PCB)
E160 / E161 Your boiler has detected a problem with the fan that safely pushes waste gases out of your home, causing the system to shut down for safety.
Your boiler has detected a problem with the fan that safely pushes waste gases out of your home, causing the system to shut down for safety.
Parts commonly replaced
- Fan unit
- PCB (Main Circuit Board)
- Wiring harness
Related codes
E163 Your boiler's temperature sensor for hot water has stopped working correctly, meaning your taps and showers may run cold or at inconsistent temperatures.
Your boiler's temperature sensor for hot water has stopped working correctly, meaning your taps and showers may run cold or at inconsistent temperatures.
Parts commonly replaced
- DHW NTC Thermistor Sensor
- Wiring Harness/Connector
Related codes
E164 Your boiler is struggling to monitor its own internal water pressure, which prevents it from heating up your home safely.
Your boiler is struggling to monitor its own internal water pressure, which prevents it from heating up your home safely.
Parts commonly replaced
- Water pressure sensor
- Wiring harness
Related codes
E167 Your boiler's internal computer has encountered a communication error and is unable to control the heating system correctly.
Your boiler's internal computer has encountered a communication error and is unable to control the heating system correctly.
What to check first
- Locate the reset button on the front control panel
- Press and hold the reset button for five seconds
- Release the button and wait for the boiler to restart
Parts commonly replaced
- Printed Circuit Board (PCB)
- Wiring harness
Related codes
E168 Your boiler has experienced an internal communication error, meaning the electronic control board isn't sure what to do next.
Your boiler has experienced an internal communication error, meaning the electronic control board isn't sure what to do next.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Wiring Harness
Related codes
E193 Your boiler has detected that water is not circulating correctly through the system before the burner ignites, often caused by trapped air or a blockage.
Your boiler has detected that water is not circulating correctly through the system before the burner ignites, often caused by trapped air or a blockage.
What to check first
- Check that all radiator valves and boiler isolation valves are fully open
- Bleed all radiators to remove any trapped air pockets
- Ensure the system pressure is between 1.0 and 1.5 bar on the gauge
Parts commonly replaced
- Circulation Pump
- Automatic Air Vent
- Main Heat Exchanger (Flushing)
Related codes
E270 Your boiler has detected that water is the not moving through the system properly, causing the unit to overheat or run without enough water.
Your boiler has detected that water is the not moving through the system properly, causing the unit to overheat or run without enough water.
What to check first
- Check if the boiler pressure needle is in the green zone (usually 1.0 to 1.5 bar) and top up using the filling loop if it is too low.
- Ensure all radiator valves and the boiler isolation valves are fully open.
- Gently bleed your radiators to remove any trapped air that might be blocking water flow.
Parts commonly replaced
- Circulation Pump
- Flow and Return Thermistors
- Heat Exchanger (Cleaning or Replacement)
Related codes
E317 Your boiler has detected an issue with the electrical power supply frequency coming into your home, which is preventing it from running safely.
Your boiler has detected an issue with the electrical power supply frequency coming into your home, which is preventing it from running safely.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Inline Surge Protector
Related codes
E321 Your boiler's temperature sensor for hot water has stopped working correctly, meaning your taps may not get warm.
Your boiler's temperature sensor for hot water has stopped working correctly, meaning your taps may not get warm.
Parts commonly replaced
- Domestic Hot Water (DHW) NTC Sensor
- Sensor Wiring Harness
Related codes
Showing 111–120 of 129
E384 Your boiler thinks it sees a flame even though it hasn't finished its startup process, causing it to shut down for safety.
Your boiler thinks it sees a flame even though it hasn't finished its startup process, causing it to shut down for safety.
Parts commonly replaced
- Flame sensing electrode
- PCB (Main circuit board)
- Gas valve
Related codes
E385 Your boiler is not receiving enough electrical power to operate safely and has shut down to protect its internal components.
Your boiler is not receiving enough electrical power to operate safely and has shut down to protect its internal components.
Parts commonly replaced
- Printed Circuit Board (PCB)
- External voltage regulator
- Internal wiring loom
Related codes
E430 Your boiler is checking if there is enough water pressure to operate safely and may have detected a temporary drop.
Your boiler is checking if there is enough water pressure to operate safely and may have detected a temporary drop.
What to check first
- Check the pressure gauge on the front of the boiler
- If the pressure is below 1.0 bar, use the internal filling loop levers to top it up to 1.5 bar
- Reset the boiler by turning the selector knob to 'R' for five seconds
Parts commonly replaced
- Filling loop
- Pressure sensor
Related codes
H.01 – .00 Your boiler has lost its internal connection to the part that controls the gas supply, prevent it from lighting safely.
Your boiler has lost its internal connection to the part that controls the gas supply, prevent it from lighting safely.
Parts commonly replaced
- Gas valve
- Printed Circuit Board (PCB)
- Wiring harness
Related codes
H.01 – .05 Your boiler has detected that water is failing to circulate correctly through the system, causing it to overheat and shut down for safety.
Your boiler has detected that water is failing to circulate correctly through the system, causing it to overheat and shut down for safety.
What to check first
- Check that all radiator valves are fully open
- Check that the boiler pressure is between 1 and 1.5 bar on the gauge
- Bleed all radiators to remove trapped air which may be blocking flow
Parts commonly replaced
- Circulation pump
- NTC thermistor (Temperature sensor)
- Central heating filter (requires cleaning)
Related codes
H.01 – .08 Your boiler is overheating or water is not moving through the system quickly enough to stay at a safe temperature.
Your boiler is overheating or water is not moving through the system quickly enough to stay at a safe temperature.
What to check first
- Check that your boiler pressure is between 1 and 1.5 bar on the digital display or gauge.
- Ensure all radiator valves are fully open to allow water to circulate.
- Reset the boiler by pressing the 'R' button or following the reset prompt on the display.
Parts commonly replaced
- Circulation pump
- Flow temperature sensor (NTC)
- Central heating filter
Related codes
H.01 – .14 Your boiler has sensed it is getting too hot too quickly, usually because water isn't moving through the system properly.
Your boiler has sensed it is getting too hot too quickly, usually because water isn't moving through the system properly.
What to check first
- Check that your radiator valves are open
- Ensure the boiler pressure is between 1 and 1.5 bar on the gauge
- Gently bleed your radiators to remove trapped air
- Reset the boiler to see if the temporary fault clears
Parts commonly replaced
- Circulation Pump
- Pump Lead
- Flow Temperature Sensor
Related codes
H.01 – .18 Your boiler has detected that water is not moving through the system properly or a sensor is giving an incorrect reading.
Your boiler has detected that water is not moving through the system properly or a sensor is giving an incorrect reading.
What to check first
- Check that your radiator valves and isolation valves are fully open
- Check the boiler pressure gauge and top up to 1.5 bar if it is too low
- Bleed your radiators to remove any trapped air pockets
- Reset the boiler by pressing the 'R' or 'Reset' button
Parts commonly replaced
- Central heating pump
- Temperature sensor (NTC thermistor)
- Main heat exchanger (flushing)
- Water pressure switch
Related codes
H.01 – .21 Your boiler is heating up too quickly when you try to use hot water, often because the water isn't flowing through the system fast enough.
Your boiler is heating up too quickly when you try to use hot water, often because the water isn't flowing through the system fast enough.
What to check first
- Check that your main water stopcock and all isolation valves under the boiler are fully open.
- Ensure your system pressure is topped up to between 1.0 and 1.5 bar on the digital display.
- Restart the boiler by pressing the ‘R’ or Reset button to see if the temporary fault clears.
Parts commonly replaced
- DHW Temperature Sensor (NTC)
- Plate Heat Exchanger
- Internal Pump
Related codes
H.02 – .02 Your boiler's internal computer brain hasn't been set up correctly or has forgotten its essential configuration settings.
Your boiler's internal computer brain hasn't been set up correctly or has forgotten its essential configuration settings.
Parts commonly replaced
- Printed Circuit Board (PCB)
- Configuration Plug
Related codes
Showing 121–129 of 129
H.02 – .03 Your boiler's computer brain is momentarily confused by its internal setup settings and cannot start correctly.
Your boiler's computer brain is momentarily confused by its internal setup settings and cannot start correctly.
What to check first
- Locate the reset button on the front control panel
- Press and hold the reset button for 1 to 3 seconds
- Wait for the boiler to restart; if the code clears, the boiler should resume normal operation
Parts commonly replaced
- Printed Circuit Board (PCB)
Related codes
H.02 – .04 Your boiler's internal computer has encountered a temporary settings glitch that is preventing it from running correctly.
Your boiler's internal computer has encountered a temporary settings glitch that is preventing it from running correctly.
What to check first
- Locate the Reset button on the front control panel.
- Press and hold the Reset button for approximately 5 seconds.
- Wait for the boiler to complete its restart sequence to see if the error clears.
Parts commonly replaced
- Main PCB (Printed Circuit Board)
- Parameter Plug
Related codes
H.02 – .06 Your boiler is struggling to operate because the water pressure is too low, often caused by a leak or air in the radiators.
Your boiler is struggling to operate because the water pressure is too low, often caused by a leak or air in the radiators.
What to check first
- Check the digital gauge or pressure dial to confirm it is below 1.0 bar
- Locate the filling loop (braided silver hose) under the boiler
- Slowly open the valves to top up the pressure to 1.5 bar, then close them tightly
Parts commonly replaced
- Filling loop
- Automatic air vent
- Pressure sensor
H.03 -.00 Your boiler is struggling to read information from its internal temperature sensors, which is preventing it from heating your home safely.
Your boiler is struggling to read information from its internal temperature sensors, which is preventing it from heating your home safely.
Parts commonly replaced
- NTC Temperature Sensor
- Flue Sensor
- Wiring Harness
Related codes
H.03 – .01 Your boiler’s internal computer is having trouble talking to its main control board, which has caused the system to stop working for safety.
Your boiler’s internal computer is having trouble talking to its main control board, which has caused the system to stop working for safety.
Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Wiring Harness
Related codes
H.03 – .02 Your boiler has lost its flame while it was running, meaning it has stopped providing heat and hot water for safety reasons.
Your boiler has lost its flame while it was running, meaning it has stopped providing heat and hot water for safety reasons.
What to check first
- Check if other gas appliances in your home, like a hob, are working to ensure gas is reaching the property.
- Verify that your prepaid gas meter has credit, if applicable.
- Restart the boiler by pressing the 'Reset' button for five seconds.
Parts commonly replaced
- Flame sensing electrode
- Gas valve
- Ignition lead
Related codes
OFF OFF OFF Your boiler has no electricity reaching the unit and is currently turned off.
Your boiler has no electricity reaching the unit and is currently turned off.
What to check first
- Check if your mains electricity is working in the rest of the house
- Ensure the boiler's fused spur switch next to the unit is switched ON
- Check your consumer unit/fuse box to see if the heating circuit has tripped
- If you have a pre-payment meter, check that you have credit available
Parts commonly replaced
- 3A Fuse
- PCB (Printed Circuit Board)
- Wiring harness
ON OFF ON Your boiler has failed to light several times and has locked itself out for safety.
Your boiler has failed to light several times and has locked itself out for safety.
What to check first
- Check if your gas supply is active and other gas appliances are working
- Ensure your prepaid gas meter has credit
- Press and hold the 'R' or reset button for 5 seconds
Parts commonly replaced
- Ignition Electrode
- Gas Valve
- Spark Leads
Related codes
ON ON ON Your boiler has detected an internal electrical communication problem between its main control components.
Your boiler has detected an internal electrical communication problem between its main control components.
Parts commonly replaced
- Low voltage wiring harness
- Main PCB (Printed Circuit Board)