BoilerFaultCodes 120 High
Boiler Fault Code 120
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 120 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 is failing to ignite because it cannot detect a flame, meaning you currently have no heating or hot water. (As reported on Sime Dewy 30/130 HE FS)
Pick your boiler brand for the 120 fix
Source
Information for the 120 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