F9 High

Boiler Fault Code F9

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code F9 appears across 7 boiler brands and 54 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler's internal computer has forgotten its settings or has developed a technical communication error, meaning it cannot safely control the heating process. (As reported on Ideal Logic+ System)

Pick your boiler brand for the F9 fix

Ferroli F9 5 models Glow-worm F9 5 models Heatline F9 4 models Ideal F9 17 models Keston F9 8 models Saunier Duval F9 6 models Viessmann F9 9 models

Source

Information for the F9 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