10 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: Promax System High Efficiency
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 |
|---|---|---|
| 41-591-90 | Promax System 12 HE Plus | 2007–2008 |
| 41-591-91 | Promax System 15 HE Plus | 2007–2008 |
| 41-591-92 | Promax System 18 HE Plus | 2007–2008 |
| 41-591-93 | Promax System 32 HE Plus | 2007–2008 |
| 41-601-21 | Promax System 24 HE Plus | 2005–2008 |
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Your boiler has lost its connection to the sensor that monitors the temperature of the water in your heating system, causing the boiler to stop working.
Your boiler has detected a problem with the sensor that monitors the temperature of the exhaust gases, causing it to stop running for safety.
Your boiler is struggling to accurately detect the temperature of your hot water supply, so it has safely shut down to prevent overheating.
Your boiler has shut down because it has detected an unsafe increase in temperature and has triggered a safety cut-out to prevent damage.
Your boiler has detected that the water pressure is too low for it to run safely and has shut down as a precaution.
Your boiler has stopped working because water is not moving through the system correctly, which could be due to a blockage or a pump issue.
Your boiler has sensed that the exhaust gases are getting too hot and has shut down as a safety precaution to prevent damage.
Your boiler has failed to light because it either cannot get enough gas or cannot detect a flame once ignited.
Your boiler has stopped working because the internal fan, which safely clears exhaust gases, isn't spinning at the correct speed.
Your boiler has sensed that water is not circulating properly before it starts the heating process, which is usually caused by an air lock or a blockage.
Not faults — these are normal operating states. Tap to expand.
BoilerFaultCodes