I have a seven-year-old GE double oven, and the top oven started malfunctioning a few months ago. When I turn it on, it initially heats to the correct temperature, then stops heating, and never heats again. So if I set it to 400 degrees Fahrenheit, it will reach that temperature (actually it will go to around 450), then stop heating, and the temperature just drops from there.
The strange thing is that the temperature sensor is working: if I shut the oven off and turn it back on, it will tell me the current temperature. (Yes, I am using a portable oven thermometer to confirm its reading.)