34 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: Greenstar 25i
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 →
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Your boiler has detected a failure in its internal safety systems which is preventing it from starting up correctly to supply heat and hot water.
Your boiler is completely unresponsive and is not receiving any electricity.
Your boiler is working fine to heat your hot water, but it is failing to turn on when your radiators request heat.
Your boiler is currently taking a short, intentional break as part of its normal operating cycle to prevent overheating.
Your boiler has detected a safety-related issue with its internal heat sensors or water flow, causing it to shut down to prevent damage.
Your boiler has experienced a sudden technical error and has locked itself to prevent damage, requiring a manual reset to attempt to clear the fault.
Your boiler has detected an internal error and has automatically paused its operation to prevent damage, requiring you to manually restart it.
Your boiler is currently set to a special testing mode used by engineers to check its performance, rather than operating in its normal heating mode.
Your boiler has automatically turned on its frost protection mode because the internal temperature has dropped close to freezing point.
Your boiler has automatically turned itself off because the water inside it has become hotter than the appliance can safely manage.
Your boiler has automatically turned itself off because the hot water inside it has become dangerously hot.
Your boiler has detected an issue with how it clears exhaust fumes, causing it to stop running for safety.
Your boiler's temperature sensor has failed or has a wiring issue, which means the system cannot safely monitor how hot the water is or provide heating and hot water.
Your boiler has switched itself off because it is getting too hot inside, usually to prevent internal damage.
Your boiler is failing to light the gas, meaning it has shut down to prevent unburnt gas from building up.
Your boiler thinks it can see a flame inside the system even though the heating is turned off, causing it to stop working for safety reasons.
Your boiler thinks it still sees a flame even though the gas supply has been turned off, which is a safety conflict.
Your boiler is not receiving any power, meaning it cannot provide heating or hot water until an electrical supply is restored.
Your boiler has suffered an internal electrical failure that is preventing it from starting up or operating safely.
Your boiler is currently waiting for a signal from your thermostat or timer to tell it that the house needs heating or hot water, but that message isn't reaching it.
Your boiler's internal control center is failing to communicate correctly, which will likely prevent your heating or hot water from turning on.
Your boiler has lost the ability to detect when you turn on a hot water tap, meaning it cannot start the heating process correctly.
Your boiler has detected that it is in an area that is too cold, so it has effectively entered a protective standby mode to prevent its pipes from freezing.
Your boiler has shut down because it is running too hot, likely due to low water pressure or trapped air in the heating system.
Your boiler is failing to light the flame, which means it has stopped working to keep you safe.
Your boiler has detected a communication error with its internal sensors or electrical connections, causing it to stop operating as a safety precaution.
Your boiler is struggling to breathe because it cannot clear out exhaust gases properly, so it has safely shut itself down to prevent any issues.
Your boiler is struggling to ignite because the internal gas system isn't communicating correctly, meaning you currently do not have heating or hot water.
Your boiler's electronic brain is failing to communicate correctly or has been damaged by moisture, causing the system to stop working as a safety precaution.
Your boiler's fan is running continuously to keep the internal temperature steady, which is a normal part of the system's operation process.
Your boiler is failing to light the flame, which means it has safely shut itself down to prevent a gas leak.
Your boiler has failed to light the flame several times and has shut down completely to prevent gas from escaping.
Your boiler has reached an unsafe temperature and has automatically shut down to prevent damage and ensure your safety.
Your boiler has detected that the water inside is dangerously overheating and is running the pump constantly to try and cool it down.
BoilerFaultCodes