Soggy bottoms

I have an electric fan cooker and a microwave with a convection fan oven, they both have the elements in the top although the big oven has heat from the sides as well.
Neither of them cook the bottoms of pies or pasties (especially frozen ready-made sausage rolls etc) which turn out partly raw.
I pre heat the ovens to temperature, so the base is hot, but they never ever cook pastry bases thoroughly, although the tops get nicely browned.
Apart from pre-cooking the bases which isn't practical when making something like an apple pie, what can I do?
Half cooked bottoms are uneatable.