The biggest problem with ovens is heat and humidity. These two elements are disaster for electrics and electronics. Thus failures are common in such equipment that has not been subjected to very rigorous pre manufacturing tests.
Derek
August 2008
You need to be able to test the circuit (when isolated) with a suitable test meter. Most folk shrink from this prospect. However, it is just possible that a corroded or bad connection could be the problem. If not the offending fan motor may have failed and needs to be replaced.