BoilerFaultCodes 20-21 High
Boiler Fault Code 20-21
Also written as 2021 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 20-21 appears across 1 boiler brand and 3 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has shut down because it has detected internal temperatures that are too high, triggered by a safety sensor to prevent overheating. (As reported on Remeha Gas 350)
Pick your boiler brand for the 20-21 fix
Source
Information for the 20-21 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