b8 High

Boiler Fault Code b8

Also written as B8 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code b8 appears across 1 boiler brand and 8 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 a broken connection or a fault with the sensor that monitors the temperature of the exhaust gases, causing the system to stop working for safety. (As reported on Viessmann Vitodens 050-W)

Pick your boiler brand for the b8 fix

Viessmann b8 8 models

Source

Information for the b8 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