BoilerFaultCodes H21-064 High
Boiler Fault Code H21-064
Also written as H21064 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code H21-064 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 has detected that the exhaust gases are getting too hot, so it has turned itself off to prevent overheating. (As reported on Ideal Mini HE)
Pick your boiler brand for the H21-064 fix
Source
Information for the H21-064 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