BoilerFaultCodes AA9999 High
Boiler Fault Code AA9999
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code AA9999 appears across 1 boiler brand and 7 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 having trouble interpreting its own internal signals, which has caused it to shut down for safety reasons. (As reported on Ariston E-Combi One 30)
Pick your boiler brand for the AA9999 fix
Source
Information for the AA9999 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