I have a GE JTP15WWWW that is overheating. It preheats fine, but then something triggers the broiler to come on and it burns everything. It doesn't do it every time, but intermittently. Unit is 13 yrs old. I had repair person tell me that it was the motherboard, but I'm not sure. The oven really hasn't been used that much even though it's 13 yrs old. It is a 30" electric wall oven. Is it worth repairing? I've priced new ovens and I'm looking at $1200 for a comprable unit.