Nearly 20 yo elect Whirlpool oven here. Sometimes it heats and regulates fine. Other times (most often) it will work fine for 15-20 minutes, but then the temperature will begin to drift down. At one hour it will be down perhaps 40 degrees from the setpoint. (I have a thermocouple mounted in the center of the oven) During this drift-down period the HEAT indication continues to cycle. The bake element no longer gets hot during that time, but the broil element will turn on for about 15 seconds every time heat is demanded. I've checked a few things. Bake element is 22 ohms, broil is 19 ohm, temp sensor is 1,100 ohms at room temp. I have 240 VAC at the line inputs. I took a look in back and didn't notice any obvious poor connections.
Is this likely a controller issue? If so, I guess the next question is, does it make sense to spend $250 to fix a nearly 20 year old electric oven? Other than this issue it works fine.
Thanks very much in advance !