24 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Pick the one you have. The fault codes, GC numbers and manual differ by type.
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 →
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Your boiler is failing to recognise that the burner has lit, preventing it from heating your home for safety reasons.
Your boiler has detected an issue with its internal ventilation fan, which means it cannot safely clear exhaust fumes and will not ignite.
Your boiler has detected a problem with the internal temperature sensor that monitors your central heating, which may stop the system from warming up properly.
Your boiler has detected that the exhaust gases are getting too hot, so it has shut down as a safety precaution to prevent damage.
Your boiler has detected that the water pressure is too low, causing it to stop working for safety.
Your boiler has too much water inside it, causing the pressure to rise to an unsafe level.
Your boiler has a fault with the domestic hot water sensor, meaning it may still provide heating but cannot accurately control the temperature of your hot water.
Your boiler has stopped working because it cannot accurately monitor the temperature of the water being heated for your radiators.
Your boiler has tried to start but could not detect a flame, likely because gas isn't reaching the burner or the ignition spark is failing.
Your boiler has shut down because it has detected it is getting too hot, often caused by a lack of water flow or trapped air.
Your boiler has stopped working because the water pressure inside your heating system has dropped too low.
Your boiler's internal water pressure is currently too high, which is preventing it from operating safely.
Your boiler has detected a communication problem with the part that monitors the temperature of your hot water, which may cause your hot water to stop working or not reach the correct temperature.
Your boiler has stopped working because it is unable to accurately measure the temperature of the water used for your heating system.
Your boiler has detected an issue with the flame and has safely shut itself down to prevent any risk.
Your boiler has detected that it is dangerously overheating and has automatically shut itself down to prevent damage.
Your boiler is failing to light the burner because it cannot detect a flame, causing the system to shut down for safety reasons.
Your boiler has detected that water is not flowing through the heating system correctly, preventing it from heating your home safely.
Your boiler's control system is struggling to read a secondary temperature sensor, which has caused it to stop heating to ensure your safety.
Your boiler has detected that the gases produced during burning are not escaping properly, so it has safely shut down to prevent the build-up of dangerous fumes.
Your boiler has detected a potential issue with the sensor that monitors the waste gases leaving the system, so it has shut down as a safety precaution.
Your boiler has detected that water is not circulating correctly or has become too hot, causing it to shut down for safety.
Your boiler has switched itself off because it is detecting a dangerous build-up of heat or a potential problem with exhaust gases.
Your boiler has failed to light the gas and has locked itself for safety, which means you currently have no heating or hot water.
Not faults — these are normal operating states. Tap to expand.
BoilerFaultCodes