Zanussi ZBF 865 overheating?

My neighbours single oven burns everything. I turn it up to 180 aand the red light comes on and stays on. If i turn it down the red light stays on until the dial reaches 50 degrees or less before I hear it click and the light goes off. I have been told there are three thermostats in this model. Any idea which it could be?
Thanks for any help. Elderly neigbour living off microwave meals at present!!