the most common fault on a fan assited oven is the element that is surrounding the fan,if you remove all the trays,at the back of the oven there is a metal plate,held in place with two or four screws,remove these to see the element,make sure you turn the power off first.check for any sign of a blow out,i.e.splits,depending on the type of heater,some come out from the inside of oven,some you will need to remove oven,s back panel,hope this helps,
gts, October 2010