Our oven, that has been flawless until now (exactly 10 yrs old),does not seem to be heating correctly. The bake element does come on for the pre-heat cycle(350f) and I have measured temperature with a heat gun after the pre-heat cycle the bottom pan is aprox 400F. I have put a ceramic bowl on the middle rack and raised the temerature to 450f after 10 minutes the small ceramic bowl only reads about 350f but after 20 minutes reads 450f. I measured the resistance of the temp probe, it was about 1600ohms after the pre heat cycle to 350f. I also have noticed a small hole 1/8" x 3/8" in the rear middle of the oven floor pan. it almost looks like it has been erroded? not sure if its a product of a short or if its supposed to be there. 
It almost seems the bottom element is not cycling properly? food seems to brown on top but not on the bottom.