BoilerFaultCodes E 21 High
Boiler Fault Code E 21
Also written as E21 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code E 21 appears across 2 boiler brands and 2 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is struggling to circulate water properly because there is too large a temperature difference between the water leaving and returning to the boiler. (As reported on Warmhaus Enerwa)
Pick your boiler brand for the E 21 fix
Source
Information for the E 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 7 July 2026