there is a main oven fan heating element in the back of the cooker around the outside of the fan you can see rotating.take the fan cover guard off (4 screws) and you will see the element mounted behind.I think this will be faulty and will need replacing.again this can be done from the inside of the oven cavity by removing the screws and gentally pulling it through the back with wires attached.SWITCH IT OFF before attempting to remove the above parts!!
ck
April 2009