The fan element on the bottom oven on our Siemens HB903 double oven has blown four or five times since we bought it in 2003. So this particular problem seems to be a good little earner for Siemens, BSH Appliances and local appliance repair firms in general (costing me well over £100 each time on average). It cost £167 the latest time (this week). The repair man couldn't get to the element from the front of the oven as he couldn't remove one of the screws fixing the fan, but he could still replace the element - from the back of the oven. He advised against using WD-40 - he did it once and regretted it due to the smell lasting ages. This problem has put me off buying Siemens ovens in future.
John
November 2011