16 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 |
|---|---|---|
| 47-310-21 | iC28 | 2015–present |
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Your boiler has lost communication with its outdoor temperature sensor, which means the system may not be able to adjust its heating efficiency based on the weather outside.
Your boiler has lost its connection with the temperature sensor that monitors the water leaving the unit, meaning it cannot safely regulate heat.
Your boiler has stopped working because it cannot get a correct temperature reading from the pipe that brings water back into the unit.
Your boiler's hot water sensor has stopped working correctly, which means the system cannot accurately measure or provide hot water.
Your boiler has lost its internal connection between its main control board and the display or smart thermostat, preventing it from receiving commands.
Your boiler has detected that the water pressure is either too low or too high, causing it to shut down for safety.
Your boiler is currently running a seven-minute self-cleaning cycle to remove air bubbles from the pipes after the system pressure was too low.
Your boiler has shut down because it has detected it is getting too hot, which is usually due to poor water circulation or a blockage.
Your boiler has shut down because the internal water temperature has become too high, often caused by a lack of water flow or a circulation error.
Your boiler has shut down because there is too much water pressure in the system, which puts unnecessary stress on the internal components.
Your boiler has detected that the water pressure is too low, causing it to slow down to protect the system.
Your boiler has lost its connection with a critical safety component or its internal wiring has developed a fault, causing the system to stop working to protect itself.
Your boiler's internal fan has stopped working, which means it cannot safely blow waste gases out of the flue and has shut down as a safety precaution.
Your boiler has tried to light itself five times and failed, resulting in a lockout to prevent unburned gas from building up.
Your boiler has stopped working because the fan that removes waste gases is not spinning at the correct speed or the main control board has developed a fault.
Your boiler has sensed that water isn't moving through the system properly and has shut down to prevent the unit from overheating.
Not faults — these are normal operating states. Tap to expand.
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BoilerFaultCodes