17 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
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's main control board has suffered an internal failure and can no longer safely operate the burner.
Your boiler's safety system is detecting a flame when there shouldn't be one, preventing it from starting up correctly.
Your boiler's reset system has detected a fault with the button itself, often because it is being held down too long or is stuck.
Your boiler's computer memory has developed a permanent internal fault and can no longer process the commands needed to fire the burner.
Your boiler has detected an unstable electrical supply, meaning the power entering the unit is either too high or too low for it to operate safely.
Your boiler has tried to start several times but keep losing its flame, so it has locked itself for safety reasons.
Your boiler has stopped working because it cannot complete its initial warm-up sequence, likely due to a disconnected internal plug or a fault with the pre-heating system.
Your boiler has stopped because it thinks it sees a flame when there shouldn't be one, which is usually caused by a dirty sensor or an incorrect air-to-fuel mix.
Your boiler's internal computer has detected an electrical fault with the valve that controls the fuel supply, causing the system to shut down for safety.
Your boiler's internal cooling and combustion fan has stopped working, preventing the burner from starting up safely.
Your boiler has detected a sensor error that means it cannot monitor the temperature of the water moving through your heating system.
Your boiler's hot water sensor is reporting an error, meaning the system cannot accurately measure the temperature of the water being stored.
Your boiler’s internal control board has suffered an electrical component failure and can no longer operate the hot water pump.
Your boiler has stopped working because it cannot detect a stable electrical connection from the mains power supply.
Your boiler has stopped working because the burner failed to light or stay lit during its startup sequence.
Your boiler is not detecting when you turn on a hot tap, so it isn't starting the process to heat your water.
Your boiler has switched itself off because it has become too hot internally, likely due to a blockage or a pump issue stopping the water from moving.
Not faults — these are normal operating states. Tap to expand.
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BoilerFaultCodes