I have a cedar hot tub which came with my house. It is heated through a heat exchanger which is fed from the boiler for the radiant heating in the house. The wiring needs to be upgraded. For the most part I understand how the system is supposed to work, with the exception of this item pictured in the photo 1 below. I'm assuming that this is some sort of thermo sensing device to prevent over heating. If this is the case I don't understand how it can work being wired into the control panel the way it is. It is wired into the switch 2 position(right side of terminal block, it is the grey wire with black tape at the end). This the same terminal that an external magnetic switch is wired to using thermostat wire. Anyone have any thoughts on this? Thanks for your help!

CJ

It should be a freeze protector.

When it gets cold enough, it closes which turns on the pump relay inside the box.

(Wired in parallel with the thermostat wiring - so either the thermostat or the freeze protector can turn on the pump).

Thanks for the input Pageup. That makes sense. I live where it gets well below freezing in the winter.

CJ