50 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: Keston System 30
The fault code is already on your display
Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →
Tap any card for details
Your boiler's electronic brains are having trouble communicating with an internal plug-in memory chip, preventing the unit from starting up.
Your boiler has lost communication with its electronic identity card, meaning the internal computer no longer knows how to operate the system safely.
Your boiler thinks it sees a flame even though it hasn't finished its start-up sequence, which is preventing it from running safely.
Your boiler has tried to light several times but cannot establish a steady flame, usually because there is no gas reaching the burner or the ignition sequence is blocked.
Your boiler thinks a flame is burning even when it shouldn't be, which is usually caused by an electrical fault or a sensor issue.
Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.
Your boiler has lost power or was switched off while it was already trying to tell you about a different fault.
Your boiler has stopped working because it cannot spin the internal fan required to safely clear exhaust gases.
Your boiler has sensed that the exhaust gases are getting too hot, which often indicates the main heat exchanger is blocked or struggling to transfer heat correctly.
Your boiler is failing to detect a flame correctly, which prevents it from firing up and providing heat or hot water.
Your boiler has stopped working because its internal computer cannot properly communicate with or control the gas valve.
Your boiler's internal computer has encountered a critical error and can no longer communicate with the rest of the system.
Your boiler has stopped working because its internal temperature sensors are giving conflicting or incorrect readings during its self-test.
Your boiler’s internal computer has detected a technical malfunction that is preventing the system from running safely.
Your boiler has become too hot because water is not moving through the system quickly enough to cool it down.
Your boiler has stopped running because the water returning to the unit is too hot, which usually means the water isn't moving through your radiators properly.
Your boiler is having trouble detecting or maintaining the correct water level, which has caused it to stop running for safety.
Your boiler has shut down because it keeps losing water pressure and has failed to stay topped up four times in a single day.
Your boiler’s internal computer has encountered a critical error and can no longer safely control the heating process.
Your boiler is struggling to keep its flame lit, which is often caused by a blocked air pipe, a frozen drain, or an issue with the gas supply.
Your boiler has identified an electrical fault with the internal sensor that monitors water temperature, causing the system to shut down for safety.
Your boiler has lost communication with the internal sensor that monitors water temperature, causing the system to shut down as a safety precaution.
Your boiler has detected a fault with the sensor that monitors your hot water temperature, meaning you likely have no hot water or the temperature is inconsistent.
Your boiler has detected an electrical fault with the sensor that manages your hot water, which usually means your taps will only run cold.
Your boiler has detected that the electrical power coming into your home is too low for it to operate safely.
Your boiler has detected an issue with the electrical power timing coming from the mains, which is preventing it from running safely.
Your boiler has lost its connection to the sensor that monitors the temperature of the water leaving the unit, causing it to shut down for safety.
Your boiler has detected that the water pressure is too low, causing it to stop working for safety.
Your boiler's control panel button is stuck or faulty, preventing the system from processing commands or resetting.
Your boiler has detected that there is too much water pressure in the system, which has caused it to shut down for safety.
Your boiler’s internal control panels are having trouble talking to each other, meaning the main computer cannot receive instructions to heat your home.
Your boiler has detected a technical fault with the sensor that monitors water temperature returning to the unit, causing the system to shut down for safety.
Your boiler has stopped working because it cannot communicate with the sensor that monitors the temperature of the water returning to the unit.
Your boiler has detected an electrical fault with the sensor that monitors exhaust gases, causing the system to shut down for safety.
Your boiler's internal computer brain is having trouble talking to the display panel on the front, which stops the system from working correctly.
Your boiler has detected an electrical fault with the sensor that monitors exhaust gases, causing the system to shut down for safety.
Your boiler has encountered a critical system error that has forced it to shut down to prevent damage or unsafe operation.
Your boiler has lost its identity because a small internal memory chip is either missing or has failed, meaning the unit doesn't know how to operate.
Your boiler has detected that there is not enough water in the system to operate safely and has shut down to prevent damage.
Your boiler has lit correctly but the flame has gone out unexpectedly, preventing the system from heating your home.
Your boiler's internal fan is not running at the correct speed or has failed to start, which means the system has safely shut down to prevent gas from entering without ventilation.
Your boiler has detected that water is not circulating correctly or a temperature sensor has failed, causing the system to shut down for safety.
Your boiler has detected a problem with the sensor that monitors water returning from your radiators, causing the system to shut down for safety.
Your boiler is having trouble communicating with the outdoor thermometer that helps it adjust to the weather, which may affect its efficiency.
Your boiler has detected that the electricity supply coming into your home is at a lower voltage than it needs to operate safely.
Your boiler's main control computer has developed an internal error and can no longer communicate with the rest of the system.
Your boiler has shut down because the water inside has become too hot, which is usually caused by a circulation problem or a blockage.
Your boiler has started an ignition sequence but lost the flame, meaning the system has shut down for safety because it cannot stay lit.
Your boiler has been manually reset too many times in a short period and has locked itself out for safety.
Your boiler has sensed a flame inside the unit when there shouldn't be one, causing it to shut down for safety purposes.
BoilerFaultCodes