b5 High

Boiler Fault Code b5

Also written as B5 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code b5 appears across 4 boiler brands and 19 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has failed to complete its initial setup process, meaning it hasn't properly cleared air from the system or finished its first startup sequence. (As reported on Viessmann Vitodens)

Pick your boiler brand for the b5 fix

Ideal b5 1 model Remeha b5 3 models Viessmann b5 9 models Worcester Bosch b5 6 models

Source

Information for the b5 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