My xr80 crane furnace will not run some times. I have looked at the red flashing light and read my code list on the back of my panel. This told me that I have an open high limit device. I checked what I think is this device and it does have continuity. I also noticed that if I turn off the power to my heater for about twenty minutes and then turn it back on it will fire up. My question is is there any other thing that can cause this to happen? And am I looking at the correct device? The device I looked at is mounted up on the fire box.