b9 High

Boiler Fault Code b9

Also written as B9 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code b9 appears across 2 boiler brands and 4 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has likely been left in a testing mode used during installation or there is a fault with the gas ignition valve. (As reported on Viessmann Vitodens)

Pick your boiler brand for the b9 fix

Remeha b9 3 models Viessmann b9 1 model

Source

Information for the b9 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