Boiler Fault Code ER 4

Also written as ER4 — same fault.

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

Fault code ER 4 appears across 2 boiler brands 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 is failing to shut off its flame properly because of a potential issue with the internal gas controls; you should turn off the gas supply at the meter immediately for your safety. (As reported on Ferroli Xignal)