BoilerFaultCodes Fault 12 / 170 High
Boiler Fault Code Fault 12 / 170
Also written as FAULT12170 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code Fault 12 / 170 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's internal computer has lost communication with a central safety component or an external controller, causing the system to shut down for safety. (As reported on Worcester Bosch Greenstar CDi Compact)
Pick your boiler brand for the Fault 12 / 170 fix
Source
Information for the Fault 12 / 170 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