you can try hitting it lightly, take a small hammer and hit it. Sometimes they lock up if it frees up just spray some lube on it and youll be good to go.

I had the exact same problem a few weeks ago!

What I have found was that if I press gently on the temperature dial the heater motor would suddenly start.So i removed the wood panel surrounding the heater controls and found that the heater unit itself was not secure properly behind the wood panel,and noticed that the dial wasn't sitting smack in the middle of where it should have been.
Put everything back in place and voilą! All done and all controls are in tip top shape!
Give it a try and good luck
Dan
Vancouver Canada