BoilerFaultCodes 65:1 High
Boiler Fault Code 65:1
Also written as 651 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 65:1 appears across 1 boiler brand and 5 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 direct heated water to either your radiators or your hot water taps because a motorized internal valve has become stuck or failed. (As reported on Viessmann Vitodens 300-W)
Pick your boiler brand for the 65:1 fix
Source
Information for the 65:1 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