64 High

Boiler Fault Code 64

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code 64 appears across 2 boiler brands 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 has detected an issue with an external control or connection, such as a faulty room thermostat or a loose link wire, which is preventing it from firing up correctly. (As reported on Sime Planet Super 4 WM)

Pick your boiler brand for the 64 fix

Gledhill 64 1 model Sime 64 4 models

Source

Information for the 64 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