AEG U3100-4-m

Here we go again!Out of my depth again.
AEG b/in double oven. Everything works except the grill and top oven. All grill elements are fine and the bottom element of the top oven is fine. there is a bullet stat at the rear left-looking from the rear- and this reads across, there are two other stats next to each other near the cooling fan, the right hand stat reads through, the left one is o/circuit. as soon as you turn the grill on the cooling fan comes on-is this right? Cannot visually see anything wrong with the selector switch and the top oven thermostat clicks and reads through with the wires removed. Any ideas anyone please.