Boiler Fault Code F.20

Also written as F20 — same fault.

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

Fault code F.20 appears across 2 boiler brands and 59 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 down because it has detected an unsafe increase in internal temperature, likely caused by a sensor fault or an issue with water flow. (As reported on Vaillant ecoTEC exclusive)