Always check for continuity across the relay terminals

this switch is mounted on the side of the burner box or near the manifold to monitor for escaping flames or excessive radiant heat

This allows for quick identification of the control voltage within a crowded panel

ensuring a precision seal between the heat exchanger and the collector box

Operating on a standard 24V control circuit

McDonnell & Miller 305200 Replacement Switch Els PW 17895 Always check for continuity acrossThe McDonnell & Miller 305200 Replacement Switch (Model number FS4 33) is a high performance SPDT (Single Pole, Double Throw) snap action assembly specifically engineered for integration with general purpose liquid flow switches. This technician grade component serves as the core electrical interface for Series FS4 3 and FS4 3T units, detecting flow velocity changes to trigger or terminate power to downstream equipment such as pumps, burners, and