Anyone having problems with top oven. Recently purchased new double oven from Neff. When I tried to use top oven to bake a sponge the outer grill comes on and burns the cake!!! The grill keeps coming on intermittently throughout. Neff engineer came out and said it was normal for grill go come on to keep the temperature. He told me NOT to use the top oven for baking (which the manual clearly says I can). Just does not make sense.