BoilerFaultCodes U4-65 Low
Boiler Fault Code U4-65
Also written as U465 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code U4-65 appears across 1 boiler brand and 1 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is still providing heat and hot water, but it has lost communication with your smart room thermostat, meaning you cannot control the temperature remotely. (As reported on Daikin D2CND)
Pick your boiler brand for the U4-65 fix
Source
Information for the U4-65 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