BoilerFaultCodesThe 6 most common faults
Your boiler has failed to ignite after several attempts, meaning it cannot provide heating or hot water until reset or repaired.
Why it happens: This fault occurs when the boiler tries to light the flame several times but fails to detect one, causing the system to shut down for safety. The most common reasons are a lack of gas supply to the unit, a worn-out ignition spark, or a faulty gas valve that isn't opening correctly. In some cases, a blocked flue or moisture on the internal components can also prevent the burner from staying lit.
Check if your gas prepay meter has credit and that the gas supply valve is openPress and hold the 'Mode' or 'Reset' knob for two secondsCheck that the white condensate pipe leaving the boiler is not frozen if it is winter
Your boiler has detected that the water inside it is getting too hot, causing it to shut down for safety.
Why it happens: This fault occurs when the water within the boiler exceeds a safe temperature limit, triggering a safety shut-off to protect the internal components. It is physically caused by a lack of water flow, often due to a broken internal pump or a blockage in the pipework that prevents heat from being carried away. In some cases, a faulty sensor may be incorrectly reporting that the system is overheating when it is actually at a normal temperature.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1 and 1.5 bar on the gaugeWait for the unit to cool down and press the reset button
Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.
Why it happens: This fault occurs when the water inside the boiler exceeds a safe temperature, triggering a safety sensor to cut the power. The most common reasons are a pump failure that stops water from moving or a blockage within the main heat exchanger that prevents heat from transferring correctly. It can also be caused by air trapped in the system or a faulty sensor providing an incorrect reading.
Check that your radiator valves are open and not turned to zeroEnsure there is enough water pressure in the system (typically between 1 and 1.5 bar)Press the reset button to see if the fault clears
Your boiler has detected that it is running much hotter than it should be and has switched itself off to prevent permanent damage.
Why it happens: This fault occurs when the boiler tries to ignite three times but fails to detect a stable flame. The most common reasons include a lack of gas reaching the burner, dirty ignition components that can't create a spark, or a faulty sensor that cannot 'see' the flame even if it has lit.
Full guide for L9Your boiler's main control computer is experiencing a communication or processing error, which has caused it to stop working for your safety.
Why it happens: This fault occurs when the internal sensors detect that there isn't enough water circulating through the pipes and radiators. The most common reason is a small leak somewhere in the system or because the radiators were recently bled, causing the overall pressure to drop below the safe operating limit.
Full guide for LEYour boiler has detected that it is getting too hot and has shut down as a safety precaution to prevent damage.
Why it happens: This fault occurs when the water temperature inside your boiler rises too quickly or exceeds a safe limit, causing a safety sensor to trip. The most common reasons are a failed pump that isn't circulating the water properly or a blockage in the pipework that is restricting flow. In some cases, it can also be triggered by air trapped inside the system or a build-up of limescale in the heat exchanger.
Full guide for H9on the Ideal Esprit HE
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Ideal shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue