Look at Apart4u web site. They have instructional videos to help with these jobs. I sounds like the fan element needs replacing
Alan D
November 2010
fan heating element blown ??.this is in the back around the fan you can see rotating.remove back panel from inside the oven cavity to expose fan and element.element can be removed and replaced from inside the oven cavity with care
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix electric cookers.