Boiler Fault Code Fast flash / Off

Also written as FASTFLASHOFF — same fault.

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

Fault code Fast flash / Off appears across 1 boiler brand and 4 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has shut itself down for safety because it has detected a significant electrical or mechanical issue with its internal components. (As reported on Worcester Bosch 28i Junior)