9 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: Greenstar 30si Compact
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 |
|---|---|---|
| 47-311-84 | Greenstar 25 Si | 2005–2013 |
| 47-311-85 | Greenstar 30 Si | 2005–2013 |
| 47-311-88 | Greenstar 25 Si | 2005–2013 |
| 47-311-89 | Greenstar 30 Si | 2005–2013 |
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Your boiler is currently struggling to measure the temperature of the water it is heating, which means it will stop providing you with hot water.
Your boiler has lost its connection to the remote programmer or thermostat on your wall, preventing it from receiving instructions on when to turn the heating on.
Your boiler has detected that the water is flowing through your hot water system faster than it can heat up, which often points to an issue with how much water is being drawn from your taps.
Your boiler is struggling to accurately measure its own temperature, so it has safely shut itself down to prevent potential damage.
Your boiler has lost the ability to measure the temperature of the water used for your radiators, so it has safely shut down to prevent overheating.
Your boiler is trying to start up but cannot light the internal flame, so it has shut itself down as a safety precaution.
Your boiler is detecting a flame inside even when it is turned off, which prevents it from starting to avoid a safety hazard.
Your boiler has detected a flame even though it has commanded the gas supply to turn off, which means it must be turned off immediately for safety.
Your boiler has failed to light the flame after several attempts and has shut itself down as a safety precaution.
Not faults — these are normal operating states. Tap to expand.
BoilerFaultCodes