Boiler Fault Code 30 - 40

Also written as 3040 — same fault.

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

Fault code 30 - 40 appears across 1 boiler brand and 3 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 a faulty internal temperature sensor that monitors the water returning from your radiators, which prevents the system from heating effectively. (As reported on Chaffoteaux Minima MX2 24FF / 30FF)