Boiler Fault Code An

Also written as AN — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026

Fault code An 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 is failing to light the flame or keep it running, which means it has safely shut itself down to prevent gas from building up. (As reported on Biasi Concept 400 20 1 Mfs)