BoilerFaultCodes 420 High
Boiler Fault Code 420
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 420 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 detected a critical internal error regarding its heat output settings and has shut down to prevent damage. (As reported on Chaffoteaux Flexiflame 140)
Pick your boiler brand for the 420 fix
Source
Information for the 420 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