I have a Kenmore electric range, model 790.94344700. I don't know how old it is; it came with the house.
One of the 9" burners has been driving me insane. It's finicky to get to the temperature I want to begin with. It's a single, standard burner, not one of the power boil, simmer, or dual size burners. Frequently it will unexpectedly jump to high heat and incinerate whatever I was cooking, even though I obviously didn't set it to high heat. Sometimes it will not turn off even though I completely turned it off, and all I can really do is flip the breaker or keep rotating it back and forth to the off position until it turns off. I also noticed just now, while moving the unit to begin inspection, that the burner was slightly warm and I could see the element faintly glowing even though I haven't used the stove in many hours and it was turned off (the "in use" indicator was off as well), so that's awesome.
My guess is that the temperature regulator in the switch has sufficiently corroded or become fouled and thus sticks, or the switch is broken in some other way. However, I don't know for sure or how to verify this. I also don't know what parts to get or where to get it in terms of replacing it.