21 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: Greenstar 30i
Pick the one you have. The fault codes, GC numbers and manual differ by type.
The fault code is already on your display
Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →
Tap any card for details
Your boiler has detected a problem with its electronic ignition system, meaning it cannot process the command to start the flame safely.
Your boiler’s internal computer has encountered a memory error and cannot safely operate the heater.
Your boiler has detected that there is not enough water circulating through the system to operate safely.
Your boiler's temperature sensor responsible for monitoring stored hot water has developed a fault, preventing it from reading the temperature correctly.
Your boiler is struggling to accurately measure the temperature of your hot water, which usually means your taps will only run cold or slightly warm.
Your boiler's internal computer has lost its connection with the main control board, preventing the system from operating.
Your boiler's main control computer is unable to communicate with its internal plug-in components, meaning the system cannot safely start up.
Your boiler is unable to detect the temperature sensor for your hot water tank, which means it doesn't know when to heat your water.
Your boiler's internal computer is having trouble communicating with its identity chip, meaning it doesn't recognize its own settings.
Your boiler has stopped working because the internal fan, which clears exhaust gases, isn't spinning fast enough to operate safely.
Your boiler's fan is spinning faster than it should, which has caused the system to shut down for safety purposes.
Your boiler has lost the signal from an external control, such as your room thermostat or programmer, preventing it from firing up.
Your boiler has detected a faulty internal temperature sensor, which means it cannot accurately measure how hot the water is and has stopped running for safety.
Your boiler has switched itself off because it has detected that it is getting far too hot inside.
Your boiler is failing to light the gas or isn't detecting that the flame has started, causing the system to shut down for safety.
Your boiler's internal computer has encountered a communication error or software glitch that is preventing it from running safely.
Your boiler is still sensing a flame even when it should be turned off, which is a safety conflict that prevents the system from starting.
Your boiler is still detecting a flame even after it should have turned off, which is a safety concern that prevents the system from running.
Your boiler's main control board is having trouble communicating with the display panel, meaning the system cannot correctly send or receive instructions.
Your boiler has been put into a temporary reset mode because the button was held down too long or pressed accidentally.
Your boiler is simply performing a temporary startup check and restarting its initialisation process.
Not faults — these are normal operating states. Tap to expand.
BoilerFaultCodes