BoilerFaultCodes FA9 Medium
Boiler Fault Code FA9
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code FA9 appears across 1 boiler brand and 1 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 connection to your smart thermostat or external heating controller. (As reported on Viessmann Vitodens 025-W)
Pick your boiler brand for the FA9 fix
Source
Information for the FA9 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 7 July 2026