Boiler Fault Code A flashing

Also written as AFLASHING — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code A flashing appears across 1 boiler brand and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler's internal thermometer is malfunctioning, meaning the system can no longer tell how hot the water is and has stopped working to keep you safe. (As reported on Alpha CD)