11 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
The fault code is already on your display
Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →
The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.
| GC number | Appliance (register name) | Produced |
|---|---|---|
| 41-406-37 | Greenstar 30CDi Classic System ErP | 2015–2019 |
| 41-406-38 | Greenstar 30CDi Classic System ErP LPG | 2015–2019 |
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Your boiler's temperature sensor for hot water has stopped working properly, meaning your taps may only provide cold or lukewarm water.
Your boiler has lost its connection to your thermostat or remote heating controller, meaning it cannot receive instructions to turn the heating on.
Your boiler's internal computer chip is missing or has lost its connection, meaning the unit cannot identify itself and has stopped working for safety.
Your boiler’s internal fan is not spinning fast enough to safely clear away exhaust fumes, which has caused the system to shut down for safety.
Your boiler has detected a faulty internal temperature sensor, which means it cannot accurately monitor the water temperature and has shut down as a safety precaution.
Your boiler has shut down because it has detected that the water inside is Getting too hot, which is a safety feature to prevent damage.
Your boiler is failing to light the gas or stay lit, which has caused it to shut down for safety.
Your boiler's internal computer has encountered a critical electronic software or hardware error that is preventing it from running safely.
Your boiler thinks it can see a flame inside the system even though it should be turned off, which is a safety conflict that prevents it from starting up.
Your boiler is still detecting a flame even though it has tried to shut off the gas, which is a safety conflict causing the system to lock out.
Your boiler has stopped because the reset button was held down for too long or pressed accidentally while the unit was running normally.
Not faults — these are normal operating states. Tap to expand.
BoilerFaultCodes