can anyone help fix my oven?

I have an AEG competence D4100 double oven. The top oven works fine. The main oven works fine upto about 150 degrees, but if it is used at 180 or over the display goes out and the oven swithces itself off. After 10 minutes, when it is cooler, the display flashes. If I press a button the oven starts working, only for the problem to repeat itself again and again. I bought a blue torpedo shaped cooling stat for the fan but my oven doesn't seem to have one of these, it may be too old or we just haven't located it! Does anyone have any advice?