Electrical component identification and wiring help

Thanks for the help. Looks like a thermister to me. I guess it could be measuring something for system heating??? It's not mounted on any of the water tanks, it's above them. My dilema is that I have three wires and only two terminals. I know the red terminal goes to one terminal.

I got everything (except this wiring) back together yesterday. Found out that I need a new rubber washer for one of the water lines. I might try it and see what doesn't work...