Gas oven never reheats

Question

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.)

FYI: I have already read these similar questions.

Answer 1

The problem was that the igniter was getting old and (presumably) failed to work under high temperature. So it ignited the gas when the oven was cold, but failed to re-ignite the gas to maintain the temperature once the oven had preheated.

The repair man said that a failed igniter often causes my problem. He was unable to explain why the igniter works by heating up and yet fails to work when hot. In addition, the the igniter is made of carborundum, so its electrical resistance decreases as the temperature increases (the opposite of metal). But replacing the igniter did fix the oven.