We turned on the oven to preheat as normal. After a while the preheated light came on as normal. A little later we noticed the top element (broiler) did not turn off. When we try and turn the oven off with the knob (switch) it still stays on. Turned the breaker off, waited several hours and turn the breaker back on. The broiler element still comes on even with the knob in the off position. Any ideas? What's it gonna cost to fix?