15 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: Greenstar i
Pick the one you have. The fault codes, GC numbers and manual differ by type.
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 critical internal error that caused it to shut down for safety reasons and will not restart on its own.
Your boiler's internal computer has developed a fault and can no longer safely control the heating or hot water functions.
Your boiler has detected a critical internal error and purposefully shut itself down to prevent damage, meaning you currently have no heating or hot water.
Your boiler has failed to light the flame, so it has safely shut itself down and requires you to manually reset it to try again.
Your boiler has detected that the exhaust gases are getting too hot and has shut down as a safety precaution to prevent damage.
Your boiler has lost the ability to accurately measure the temperature of the hot water, which typically results in the system stopping water heating to prevent potential overheating.
Your boiler has lost its digital connection to the wireless thermostat or timer controller, meaning it no longer knows when to turn your heating on or off.
Your boiler's internal computer is failing to communicate with a small memory chip that stores its specific operating instructions.
Your boiler is failing to ignite because it is not receiving enough gas, or its waste pipe or exhaust flue is blocked, meaning it cannot operate safely.
Your boiler's electronic brain is missing a crucial identification chip that tells it how to operate, so it has safely shut itself down until the part is properly installed.
Your boiler has detected that the burner is still trying to stay lit even though it should have turned off, which suggests a potential issue with how it manages the fuel supply.
Your boiler has failed to light the flame after several attempts and has safely shut itself down to prevent a gas buildup.
Your boiler has completely lost power and is not showing any lights or signs of life.
Your boiler has lost all power and is completely unresponsive, meaning it is currently unable to provide any heating or hot water.
Your boiler is providing hot water as normal, but there is a communication issue preventing the heating from turning on when you use your thermostat.
Not faults — these are normal operating states. Tap to expand.
BoilerFaultCodes