I have never seen a thermal switch on a vacuumn motor. there will be on on the unit somewhere but ON the motor? Don't think so. You did not mention how old the unit is , or if you use it a lot. I serviced car washes and they replaced the vacumn motors about twice a year because of the use. My central vac is 20 years old and no trouble. You could have a bad switch or bad motor or even the plug that plugs the unit into could be loose and arking. My central vac starts when you plug it ( the hose) into the inlet. Could you have a low voltage wire loose. How many inlets do you have and does it work the same at every one? Plug the vac into an extension cord just for the heck of it from a differant outlet. Any better? So many questions. A filter or plugged hose has nothing to do with it running or not.