b18 High

Boiler Fault Code b18

Also written as B18 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code b18 appears across 4 boiler brands and 6 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has reached an excessively high temperature and has shut down as a safety precaution to prevent overheating. (As reported on Vokera Pinnacle)

Pick your boiler brand for the b18 fix

Atag b18 1 model Ideal b18 1 model Johnson Starley b18 3 models Vokera b18 1 model

Source

Information for the b18 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