F5 High

Boiler Fault Code F5

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code F5 appears across 9 boiler brands and 73 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has lost its ability to monitor the temperature of the water returning from your radiators, often causing it to shut down to prevent damage. (As reported on Ideal Logic+)

Pick your boiler brand for the F5 fix

Alpha F5 4 models Ferroli F5 8 models Glow-worm F5 11 models Heatline F5 10 models Ideal F5 17 models Keston F5 8 models Saunier Duval F5 6 models Vaillant F5 2 models Viessmann F5 7 models

Source

Information for the F5 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