b4 High

Boiler Fault Code b4

Also written as B4 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code b4 appears across 3 boiler brands and 15 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has not been fully configured for operation or there is a communication problem between the internal controls and the burner assembly. (As reported on Viessmann Vitodens)

Pick your boiler brand for the b4 fix

Ideal b4 1 model Viessmann b4 8 models Worcester Bosch b4 6 models

Source

Information for the b4 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