Boiler Fault Code A-A5

Also written as AA5 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code A-A5 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 has detected that the water temperature has risen too quickly or reached an unusually high level, causing it to shut down to prevent overheating. (As reported on Worcester Bosch Greenstar 8000 Life/Style)