Boiler Fault Code On Flash Flash

Also written as ONFLASHFLASH — same fault.

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

Fault code On Flash Flash 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 is running without enough water inside, which means it cannot safely heat your home and has shut itself down to prevent damage. (As reported on Potterton Promax 15/2 HE Plus)