There should be an obvious location where the combustion happens. Somewhere on that piece, you'll see a thing a little larger than a nickel with wings, held on with two screws. What someone called a "fuse" is actually a thermostat. Google for it and you'll find images [link|http://www.applianceaid.com/thermo.html|here] and [link|http://z.iwethey.org/forums/render/content/new?contentid=237522|here]. They cost a couple of bucks each. Cheap enough to be worth replacing just to see if it works.
The hard part is that you may have one around the front of the tub support behind the door. You may have to remove the entire cover to get to it. (Yes, I know more about this than I'd like to.)