Boiler Fault Code 4.2

Also written as 42 — same fault.

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

Fault code 4.2 appears across 1 boiler brand 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 has shut down because its internal temperature has become too high, often caused by a lack of water flow or a blockage. (As reported on Ideal Logic Code Combi ESP1)