A 40 High

Boiler Fault Code A 40

Also written as A40 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code A 40 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 main internal computer is experiencing a critical error, which has caused the system to shut down for safety reasons. (As reported on Chaffoteaux Minima HE)

Pick your boiler brand for the A 40 fix

Chaffoteaux A 40 1 model

Source

Information for the A 40 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 7 July 2026