BoilerFaultCodes 6-5 Medium
Boiler Fault Code 6-5
Also written as 65 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 6-5 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 having trouble communicating with your wall-mounted thermostat, which is preventing it from knowing when to turn the heating on. (As reported on Ideal Logic Air)
Pick your boiler brand for the 6-5 fix
Source
Information for the 6-5 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