25 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: Keston S-Series 55
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 |
|---|---|---|
| 41-930-10 | C 55P | 2002–present |
Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.
Tap any card for details
Your boiler has detected that the water inside the system is dangerously hot and has shut itself down to prevent damage or potential overheating.
Your boiler has detected that the water returning to it has become dangerously hot, so it has safely shut down to prevent damage.
Your boiler has detected that hot water is flowing in the wrong direction, indicating a potential issue with your heating system's circulation or internal sensors.
Your boiler is overheating because water isn't moving through the system fast enough, likely due to trapped air or a blockage in your pipes.
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Your boiler has stopped working because it cannot communicate with the internal air circulation fan, which prevents the heating process from starting safely.
Your boiler has detected that the internal fan responsible for moving air is not communicating correctly with the main computer, preventing the boiler from firing up safely.
Your boiler has detected that the water is not circulating properly around your heating system, so it has shut down to prevent damage.
Your boiler is temporarily paused because it is waiting for its internal air extraction system to spin up correctly before it safely ignites.
Your boiler is detecting a flame inside when it should be turned off, which is a safety issue that requires the system to be shut down.
Your boiler is failing to light because it cannot detect a flame, meaning you currently have no heating or hot water.
Your boiler is failing to light the flame because it cannot properly control the flow of gas.
Your boiler has detected that the power was turned off and back on again while it was already trying to deal with a fault, causing the system to lock itself for safety.
Your boiler's main computer brain is experiencing an internal error and cannot operate safely, meaning you currently have no heating or hot water.
Your boiler has detected that it is getting dangerously hot and has shut itself down to prevent damage or fire risk.
Your boiler has stopped working because it has detected that the water inside is significantly hotter than it should be.
Your boiler has shut down because the water returning to it is much hotter than it should be, suggesting the pump or water flow through your radiators is blocked.
Your boiler is shutting down because the water inside isn't moving fast enough to carry the heat away, causing the temperature to spike dangerously.
Your boiler has stopped working because the internal component responsible for pushing combustion gases out of the flue cannot turn.
Your boiler has detected that the water inside the unit is not moving fast enough, meaning it is getting too hot, too quickly.
Your boiler has stopped working because one of its internal temperature sensors is giving a false reading due to an electrical connection issue or a faulty sensor part.
Your boiler has detected a faulty signal from a sensor that monitors the temperature of the water returning to the system, causing it to stop working for safety reasons.
Your boiler has lost signal from the temperature sensor that monitors the water circulating through the system, causing it to stop.
Your boiler has lost the signal from one of its internal temperature sensors, so it has safely shut down to prevent overheating.
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
BoilerFaultCodes