37 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: Greenstar 24i
This boiler uses indicator light combinations
Note which lights are on, off, or flashing and at what speed. Match the combination to the cards below. Do not reset until you have noted the pattern. How to read fault codes →
Tap any card for details
Your boiler has detected an internal sensor failure and has stopped working to prevent damage or overheating.
Your boiler has detected a problem with one of its internal temperature sensors and has stopped working as a safety precaution.
Your boiler has detected an electrical fault involving a blown fuse on the internal control board, which prevents the unit from starting safely.
Your boiler's external or built-in heating timer is experiencing a communication or hardware malfunction, preventing it from correctly signalling when the heating should turn on or off.
Your boiler is struggling to detect the flow of water through the system, which means it cannot safely turn on your heating or hot water.
Your boiler has lost the signal from the sensor that monitors your hot water temperature, meaning the system cannot accurately heat your taps.
Your boiler's intake filter is blocked or restricted, preventing the fan from pulling in the correct amount of air for safe combustion.
Your boiler is failing to light the burner because it cannot detect the ignition spark, meaning you currently have no heating or hot water.
Your boiler has detected that the internal safety valve meant to release excess pressure has been triggered, which often causes water to leak or drip from the pipe outside your home.
Your boiler has detected an issue with the internal fan or the way it clears exhaust gases, so it has shut down to keep you safe.
Your boiler is detecting an issue with the fuel supply or the internal gas pressure, which has caused it to stop working to keep your home safe.
Your boiler has detected that it cannot ignite or maintain the flame necessary to heat your water or home safely.
Your boiler is failing to ignite its burner, which means it cannot produce any heat or hot water because it has detected an issue with the fuel or ignition process.
Your boiler has detected an issue with the way fuel is being supplied to the burner, which means it has safely shut itself down to prevent it from running incorrectly.
Your boiler is failing to detect the airflow needed for safe operation, so it has shut itself down to prevent ignition.
Your boiler is failing to light the flame because the internal electrical connection responsible for triggering ignition is likely faulty or disconnected.
Your boiler has detected an internal issue with how heat is transferred between the burner and your water, meaning it has shut itself down to prevent damage.
Your boiler has detected an issue with the protective insulation lining inside the combustion chamber, which is a safety-critical part that keeps the heat contained.
Your boiler is struggling to remove trapped air from the system, which can prevent heat from circulating properly to your radiators.
Your boiler's water circulation pump or its electrical connection has failed, meaning your heating and hot water cannot function because the system can no longer push hot water around your radiators and taps.
Your boiler's built-in pressure tank is no longer able to manage the expansion of water as it heats up, which is causing your system pressure to fluctuate and force the boiler to shut down.
Your boiler's internal computer is experiencing a communication error and is unable to safely coordinate the heating and hot water process.
Your boiler is struggling to detect or control the flow of hot water, which likely means you will have no hot water coming out of your taps or shower.
Your boiler has detected that the internal fan responsible for safely venting exhaust gases is not spinning or operating correctly, causing the system to shut down for safety reasons.
Your boiler has detected that it is running too hot and has automatically switched itself off to prevent potential damage or overheating.
Your boiler has detected an issue with the internal seals designed to keep combustion gases trapped safely inside the unit.
Your boiler has failed to ignite because it cannot detect a flame, meaning it has safely shut itself down to prevent gas from building up.
Your boiler is failing to detect the flow of water needed to fire up and provide heating or hot water.
Your boiler is failing to ignite because it cannot correctly access or regulate its gas supply.
Your boiler is failing to ignite because it cannot draw the gas supply it needs to stay running.
Your boiler has detected a loose or faulty temperature sensor connection, meaning it does not know how hot the water is and has safely shut down to prevent overheating.
Your boiler has stopped working because it cannot detect a flame, meaning it is currently unable to safely ignite fuel for your heating and hot water.
Your boiler is struggling to read its own water temperature, so it has safely shut itself down to prevent potential overheating.
Your boiler is struggling to manage the water pressure within the system, which typically means a small internal pressure-balancing component is failing or requires adjustment.
Your boiler has failed to start up or stay burning, so it has purposefully shut itself off to prevent gas from building up.
Your boiler has completely lost power and is unable to turn on, likely due to a blown fuse or a failure in the electrical control board.
Your boiler has detected that it got too hot and has automatically shut itself down to prevent damage or fire risk.
Not faults — these are normal operating states. Tap to expand.
BoilerFaultCodes