F9 High

Boiler Fault Code F9

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code F9 appears across 8 boiler brands and 52 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected an issue with its internal sensor that monitors water pressure, preventing it from heating up. (As reported on Glow-worm Xtramax HE)

Pick your boiler brand for the F9 fix

Ferroli F9 1 model Glow-worm F9 4 models Heatline F9 3 models Ideal F9 21 models Keston F9 1 model Saunier Duval F9 3 models Viessmann F9 18 models Zanussi F9 1 model

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 31 August 2026