Same thing happened to mine last week.The symptoms were that the grill element was heating and the fan was blowing but the oven did not reach more than a warm temperature.turned out to be the fan element.
Thats the cicular element behind the rear heat panel in the back of the oven.
It was a fairly easy self repair.I got the replacement part from a local supplier but plenty available on the net (price between £25-30).
Please make sure you have turned off the main power supply before attempting this repair.
You need to remove the outside back panel as well as the shelves and rear heat panel inside the oven then its just a case of unclipping the three terminals from the back of the element and removing the two holding nuts.The old element just slides out from the inside.Replace with new element and re assemble.Again, please make sure you have turned off the main power supply before attempting this repair.
best of luck!
phil.
February 2007