Boiler Fault Code 4.F

Also written as 4F — same fault.

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

Fault code 4.F appears across 2 boiler brands 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 performing a routine automatic cleaning and filling cycle of its internal drainage system, which is a normal process and not actually a fault. (As reported on Worcester Bosch Greenstar CDi Compact)