I had an interesting experience over the last few days. My shop is our attached 2-car garage. Monday morning about 7 I went out there to discover the shop was incredibly hot and the Hot Dawg heater going full bore. I quickly climbed up and shut off the heater. The instant read meat thermometer said it was 117° F out there! I immediately suspected the thermostat and had a look at it. It's a non-programmable low-temp thermostat intended for out buildings and green houses. Pretty basic. No batteries, just a bi-metallic strip, a magnet and a leaf switch in a glass vial. I checked it out and cleaned the sawdust out of it. After cooling off the shop, did some testing. It all seemed to work fine so I set it at 50° and went in the house. Went out to run some errands and came back about 3 hours later. It was only 105°F this time. New thermostat this morning and so far so good.
If you have a T-stat in your shop, it might not hurt to look at it and make sure it's clean and working well.