Boiler Fault Code A 39

Also written as A39 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026

Fault code A 39 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 Your boiler's main internal computer is failing to communicate properly, which has caused the system to shut down for safety precautions. (As reported on Chaffoteaux Minima HE System 24)