Boiler Fault Code L F (flashing)

Also written as LFFLASHING — same fault.

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

Fault code L F (flashing) appears across 1 boiler brand and 2 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is failing to light the gas flame after three attempts, which means it has safely shut itself down to prevent a build-up of unburnt gas. (As reported on Ideal Icos)