Boiler Fault Code Flash Off On

Also written as FLASHOFFON — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026

Fault code Flash Off On appears across 3 boiler brands 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 has detected that it reached a dangerous temperature and has safely shut itself down to prevent damage. (As reported on Potterton Promax Heat Only)