BoilerFaultCodes H21-048 High
Boiler Fault Code H21-048
Also written as H21048 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code H21-048 appears across 1 boiler brand and 6 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler's fan unit is failing to spin or communicate correctly, which forces the boiler to shut down to prevent unsafe combustion. (As reported on Ideal Mini HE)
Pick your boiler brand for the H21-048 fix
Source
Information for the H21-048 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