BoilerFaultCodes F.91 High
Boiler Fault Code F.91
Also written as F91 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code F.91 appears across 2 boiler brands and 24 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 your hot water cylinder because a sensor has developed an electrical fault. (As reported on Glow-worm Energy)
Pick your boiler brand for the F.91 fix
Source
Information for the F.91 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