52 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.
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
The main computer boards inside your boiler have stopped talking to each other, causing the system to shut down for safety.
Your boiler has failed to light or stay lit, meaning your heating and hot water have stopped working to keep the appliance safe.
Your boiler detects a flame when there should not be one, causing it to shut down for safety.
Your boiler has stopped working because it has tried to light several times but the flame keeps going out.
Your boiler's internal computer has failed a self-diagnostic check and cannot operate for safety reasons.
Your boiler is failing to confirm that a flame has been lit safely, so it has shut down as a precaution.
Your boiler has failed an internal safety test related to the flame detection system and cannot start for safety reasons.
Your boiler has shut down because it has detected that the internal water temperature has become too hot.
Your boiler has stopped working because its internal computer has detected a problem with how it manages the gas flow.
Your boiler has detected a problem with its internal fan system, which means it cannot safely move gases out of the flue and has shut down as a precaution.
Your boiler has stopped working because the fan, which safely pushes exhaust fumes outside, has encountered a physical obstruction or has stopped spinning correctly.
The main component that blows air through your boiler has stopped spinning or is struggling to move, causing the system to shut down for safety.
The fan that moves waste gases out of your boiler has stopped working properly, preventing the boiler from firing up for safety.
Your boiler has detected a blockage or a technical issue within the flue pipe or air intake system that is preventing it from starting up safely.
Your boiler has detected an issue with how exhaust gases are being cleared, which is preventing it from running safely.
Your boiler is struggling to push waste gases out through the exhaust pipe, often due to a blockage or a component failure in the flue system.
Your boiler is struggling to maintain a stable flame during low-power operation, which may cause it to shut down for safety.
Your boiler is struggling to burn gas correctly when running at full power, causing it to shut down for safety.
Your boiler's internal computer has detected an unusual signal from the flame, causing the system to shut down for safety purposes.
Your boiler has detected that the water pressure is too low, meaning there isn't enough water inside the system for it to run safely.
The water pressure inside your boiler is too low for it to operate safely, and the system needs to be topped up.
Your boiler has stopped working because it cannot accurately detect if there is enough water pressure in the system to operate safely.
Your boiler has detected a blockage or a fault in the flue pipe that is preventing exhaust fumes from escaping safely while the system is running at low power.
Your boiler has detected an issue with how exhaust gases are being cleared through the flue while running at high power.
Your boiler's internal computer has detected an electrical fault within its circuit board that it cannot correct itself.
Your boiler's main internal computer has lost contact with the fan that manages exhaust gases, forcing the system to shut down for safety.
Your boiler's internal computer parts have stopped talking to each other, meaning the unit cannot function or follow instructions.
Your boiler's computer system is currently confused and does not know how to correctly control your heating and hot water.
Your boiler's electronic control system has encountered an internal communication error and cannot safely manage the heating process.
Your boiler has detected a sensor problem that monitors the temperature for your central heating, preventing the system from warming up your home.
Your boiler has detected that the water in your central heating system is getting too hot, causing it to shut down for safety.
Your boiler has detected that the water temperature leaving the unit is significantly different from the water returning to it, suggesting a circulation problem.
Your boiler is struggling to open an internal valve correctly, which is preventing the system from heating your home or water properly.
Your boiler has detected a fault with the sensor that controls the temperature for your main heating circuit.
The boiler's sensor that monitors the temperature of the water returning from your radiators has developed a technical fault, causing the system to stop working for safety.
Your boiler has shut down because the water returning from your radiators has become too hot, usually due to a lack of water flow through the system.
Your boiler has detected that the water isn't circulating correctly through the system, meaning the difference in temperature between the water leaving and returning is too high.
Your boiler has detected an internal electrical communication error between its main control boards, preventing it from starting up correctly.
Your boiler has detected an issue with the sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety.
Your boiler has detected that the main heating component is becoming blocked with debris or limescale and needs a professional service.
Your boiler has failed to complete its internal safety and efficiency set-up, meaning it cannot verify that it is burning gas correctly.
Your boiler has tried and failed to adjust its own combustion settings too many times and has locked itself out for safety.
Your boiler has detected an issue with the quality of the combustion gas and has shut down as a safety precaution.
Your boiler has failed its internal self-tuning process and has locked out to ensure it doesn't burn gas inefficiently.
Your boiler has shut down because it has detected an issue with the air and gas mixture required for safe combustion.
The boiler has detected an internal logic error during its self-test and has stopped working to prevent damage.
Your boiler has encountered an internal electronic communication error that prevents it from starting correctly.
Your boiler has been manually reset too many times in a short period and has locked itself as a safety precaution.
Your boiler has detected that the water pressure in the heating system is too low to operate safely.
Your boiler's internal computer chips are struggling to talk to each other because their software versions do not match.
Your boiler's internal computer clock has developed a fault, which means it can no longer keep track of its timing functions.
Your boiler is not broken, but it has reached its scheduled maintenance interval and requires a professional service to ensure it continues to work safely and efficiently.
Not faults — these are normal operating states. Tap to expand.
Monthly cover means no unexpected bills when your boiler breaks down.
Affiliate links. We may earn a commission at no extra cost to you.
BoilerFaultCodes