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 2 boiler brands and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning The internal computer that controls your boiler has detected a critical hardware failure and is unable to operate safely, causing the system to shut down. (As reported on Chaffoteaux Minima HE System 24)

Pick your boiler brand for the A 40 fix

Ariston A 40 2 models Chaffoteaux A 40 3 models

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 31 August 2026