BoilerFaultCodes UA-66 High
Boiler Fault Code UA-66
Also written as UA66 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code UA-66 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's internal memory chips are having trouble communicating with each other, meaning the control board doesn't recognise the boiler's specific settings. (As reported on Daikin D2CND)
Pick your boiler brand for the UA-66 fix
Source
Information for the UA-66 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