BoilerFaultCodes MAIN FLOW SWITCH CLOSED High
Boiler Fault Code MAIN FLOW SWITCH CLOSED
Also written as MAINFLOWSWITCHCLOSED — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code MAIN FLOW SWITCH CLOSED appears across 1 boiler brand and 1 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler thinks water is moving through the pipes when the pump is actually off, which is preventing it from starting up safely. (As reported on Ariston Egis 24 MFFI)
Pick your boiler brand for the MAIN FLOW SWITCH CLOSED fix
Source
Information for the MAIN FLOW SWITCH CLOSED 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 27 April 2026