Hi. Mother's fan oven burnt her latest effort so next day I put a thermometer in first. Set the temp to 170 but the thermometer shot up to 250. Turned it off and cooked in the smaller (non-fan) oven above the main oven but this time the thermometer read less than the temperature I'd set. For the moment, my question is this: for a cooker with 2 ovens are there 2 separate and distinct thermostats?