BoilerFaultCodes Flash once per second High
Boiler Fault Code Flash once per second
Also written as FLASHONCEPERSECOND — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code Flash once per second appears across 1 boiler brand and 1 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has stopped working because it has failed to light or has detected a dangerous build-up of heat. (As reported on Worcester Bosch 24si II)
Pick your boiler brand for the Flash once per second fix
Source
Information for the Flash once per second fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026