This flow sensor ensures that the circulation pump delivers a sufficient flow of water to the heater to prevent overheating. If the flow is sufficient, the magnet sticks against the sensor rod and the flow information is sent to the control system.

This Harwil brand detector has a 1/2" TPM thread that screws into a tee or heater union. The stem length is suitable for 1.5-inch or 2-inch pipe sizes (48 to 63 mm diameter). It is designed for a maximum current of 0.5A.

This reed flow switch has a 1/2" MPT thread, and is designed for 1 ½" and 2" pipe fittings.

A very common component on many spas with low flow heating systems. Fits 1/2" NPT threaded pipe work and connects to the PCB. Installation is before the heater usually in a threaded tee fitting. Detects water flow allowing the heater to function correctly. No cable supplied.