I figured out my problem. The reason it was "intermittent" is because it only happened when I had two baking sheets side-by-side in the oven. They essentially divided the oven into two volumes, one below the baking sheets containing the bake heating element, and the other above the baking sheets containing the temperature sensor. The bake element would stay on, and the bottom volume would become very hot, because the top volume would remain much cooler and that is where the sensor is.

I have a GE JTP15 wall oven that intermittently overheats. If I set it to Bake at 350 degrees, the bake element will turn on, the oven-temp readout will increment, and when the readout reaches 350 the oven will beep to indicate that the target temperature has been reached. All perfectly normal so far. From that point, however, the oven will then either continue to operate properly (i.e. holding the target temp with the bake element cycling on and off), OR sometimes the bake element will cycle on and then stay on until I notice the oven is overheating and I press the off button. When the oven overheats, the thermometer I have hanging in the oven might register 500 degrees while the oven-temp readout still displays 350 degrees.

I replaced the temperate sensor and the ERC with GE renewal parts, but the problem persisted.

I removed the screen in front of the fan intake. It was quite dirty. The problem persisted.

I checked the resistance of the temperature sensor, both from the ERC (i.e. including the wiring) and at the sensor itself, and both measured correctly at 1100 ohms.

Can anyone think of what other part could be failing? The only other parts are the fan-limit and temp-limit switches, but I can't see how they would figure into this behavior.

The only explanation I can think of is that the bake switch in my new ERC is getting intermittently stuck closed (i.e. calling for heat). Has anyone heard of bake switches getting damaged in this way by excessive heat in the control compartment? I'm thinking that perhaps my new ERC got damaged when I operated the oven before removing the dirty screen in front of the cooling-fan intake. Does that sound plausible?

Thanks,
-jkd