Snap disk thermostat 8$-20$ from the plumbing supply store or online. You can get a cheaper one with a fixed temperature or spend a little more for an adjustable one. If you go to the plumbing store ask for one that has the temperature range you want. It needs to open on temperature rise (turn off when it gets hot), close on fall (turn on when cold) and be self resetting. I had to buy several at a