[arcticdude]

If it's a 431, they'll be screwed into the side of the tank next to the burner assembly. You may just have an overtemp switch failing, though. Those are under the plate (~4"x4" sq) mounted immediately above the burner. Remove the corner cover and everything else will be visible. Meaning the external portions of the elements and the aforementioned plate will be visible. You could also check for incoming voltage under the small plate where the 120 comes into the unit.