BoilerFaultCodesThe 6 most common faults
Your boiler has detected trapped air or a blockage that is stopping water from flowing through your heating system correctly.
Why it happens: This fault occurs when air becomes trapped inside the boiler's internal pump, preventing it from effectively pushing water around your radiators. The most common reason is a buildup of air pockets following a system drain-down or a failure of the automatic vent that is supposed to release these gases. In some cases, it can also be triggered by a heavy buildup of sludge or debris that has physically blocked the water's path.
Check that your boiler pressure is between 1.0 and 1.5 barBleed your radiators using a radiator key to remove trapped airEnsure all radiator valves and isolation valves under the boiler are fully openReset the boiler using the selector switch
Your boiler has stopped working because the internal pump, which moves hot water around your pipes and radiators, is either jammed or has suffered an electrical failure.
Why it happens: This fault occurs when the pump responsible for moving water through your heating system fails to spin or communicate with the main control board. The most common cause is internal debris or 'sludge' from the radiators jamming the pump's moving parts, though it can also be triggered by a failure in the motor's electrical components. As the water cannot circulate, the boiler shuts down to prevent itself from overheating.
Full guide for 60Your boiler has detected a communication error between its internal temperature sensors, which means it cannot safely monitor the water temperature and has shut down as a precaution.
Why it happens: This fault occurs when the boiler's control board receives conflicting or missing data from the internal sensors that monitor water temperature. The most common reason is a physical failure of the thermistor sensors themselves or a loose connection in the wiring harness that links them to the main computer. Because the boiler can no longer verify if the water is at a safe temperature, it shuts down to prevent overheating.
Full guide for 70Your boiler's internal thermometers are misreading the temperature or have failed, which has caused the system to shut down for safety.
Why it happens: This fault occurs when the boiler's control board detects that the temperature sensors (NTC thermistors) are sending conflicting information or no signal at all. The most common reason is a physical failure of the internal sensor probes, but it can also be caused by loose wiring or mineral buildup on the sensors preventing them from reading heat levels accurately.
Full guide for 75Your boiler's internal thermometers are misreading the temperature or have failed, which has caused the system to shut down for safety.
Why it happens: This fault occurs when the boiler's control board detects that the temperature sensors (NTC thermistors) are sending conflicting information or no signal at all. The most common reason is a physical failure of the internal sensor probes, but it can also be caused by loose wiring or mineral buildup on the sensors preventing them from reading heat levels accurately.
Full guide for 76Your boiler is simply letting you know that its annual routine service is now due to ensure it continues running safely and efficiently.
Why it happens: This code appears because the boiler's internal clock has calculated that 12 months have passed since its last professional maintenance check. It is a programmed timer meant to prompt you to book a Gas Safe engineer to keep your warranty valid and the system safe. The boiler hasn't actually broken down; it is simply a proactive reminder to ensure the internal components are cleaned and tested.
Full guide for SRon the Alpha E-Tec, E-Tec Plus, Evoke
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Alpha shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue