BoilerFaultCodes Fault 12 / 171 High
Boiler Fault Code Fault 12 / 171
Also written as FAULT12171 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code Fault 12 / 171 appears across 1 boiler brand and 1 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has lost communication with its internal electronic controls or a safety switch has triggered to prevent overheating. (As reported on Worcester Bosch Greenstar CDi Compact)
Pick your boiler brand for the Fault 12 / 171 fix
Source
Information for the Fault 12 / 171 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