BoilerFaultCodes AA 9977 High
Boiler Fault Code AA 9977
Also written as AA9977 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code AA 9977 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 computer is experiencing an internal processing error and cannot safely manage the heating system. (As reported on Ariston Clas One)
Pick your boiler brand for the AA 9977 fix
Source
Information for the AA 9977 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