Boiler Fault Code Fast flash

Also written as FASTFLASH — same fault.

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

Fault code Fast flash appears across 2 boiler brands and 24 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 a critical internal fault and has locked itself out to prevent damage or unsafe operation. (As reported on Worcester Bosch Greenstar 12Ri)