Hygena cooker problem

Hi all, I have a fault with a Hygena APL3127 built in cooker. The grill doesn't heat up hardly at all but the oven does. I think that the same element does both so I assume that the element is not faulty. The same control sets the heat for both the grill and oven, so again assume the switch is ok. I have come to the conclusion that it is the thermostat but would like soemone to verify my diagnosis please.

kind regards

The chances are the t/stat is bi passed when the grill is selected. I think the grill selector or t/stat could have a switch piggy backed on to select grill only.
Sorry do not have circuits.