18 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: Greenstar 28i Junior
Pick the one you have. The fault codes, GC numbers and manual differ by type.
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 has stopped working because it has detected a safety issue and locked itself to prevent damage.
Your boiler is temporarily limiting its power output because it is producing more heat than your radiators or taps can currently take away.
Your boiler has completely lost its electrical power supply, meaning it has shut down and cannot provide heating or hot water.
Your boiler has detected that it is running without enough water inside, which is often caused by a leak or a pump that has jammed or failed.
Your boiler has lost its connection to your external room thermostat or heating controls, meaning it doesn't know when to turn on or off.
Your boiler has lost the electronic signal from your thermostat or internal programmer, meaning it doesn't know when to turn on for heating.
Your boiler is struggling to detect the flow of water for your hot water taps due to a faulty sensor or internal control issue.
Your boiler has safely shut down because it failed to light or detected an internal safety problem.
Your boiler has detected a safety lockout, which usually points to an issue with airflow, the flue, or internal sensors, causing it to shut down to protect your home.
Your boiler has detected an internal control setting issue with the gas valve switch, which prevents it from operating safely.
Your boiler has stopped working because an internal safety fuse has failed, cutting off power to the system's control board.
Your boiler has stopped working because an internal electrical fuse has blown, cutting off the power needed for it to operate.
Your boiler's burner is staying switched on even when no heating or hot water has been requested, which usually points to an internal control board issue.
Your boiler has temporarily stopped because it detected that the internal water temperature is getting too hot.
Your boiler is not heating the water up enough because it is either not getting enough gas or a vital internal part is stuck.
Your boiler is still providing hot water normally, but it is not responding to your heating controls or timer to warm up your home.
Your boiler is still keeping your home warm, but it has stopped heating up your water for taps and showers.
Your boiler has completely lost electrical power and is not responding at all, even when you turn the heating or hot water on.
Not faults — these are normal operating states. Tap to expand.
BoilerFaultCodes