I have a fault on my built in whirlpool AKP510 oven. Last night when cooking, I noticed a burning smell after the oven had been on for 15 minutes. I switched it of to let it cool and then put the oven on a low setting to see if the thermostat was cutting out. The stat light cut out when the temp was reached, but the element continued to heat up. Is this a thermostat problem or something else?