This Siemens IQ500 (HB5D20F0 MB535A0S0B/52) built-in double oven was purchased just under 2 years ago. Functionally it is perfect except for the main oven when used in fan assist mode. On conventional mode, the temperature appears uniform throughout the oven and cooks perfectly, but when on fan assist mode, the temperature on the right hand side is slightly hotter than that on the left. The difference increases with temperature, but typically at 200deg C, the difference between right and left is around 15deg. Thus when used on fan assist mode, sometimes food requires occasional rotating to avoid over cooking on the right hand side. 

Siemens Bosch engineer investigated, and replaced the rear fan. On his last visit, still under warranty, the Bosch engineer found no obvious defect that might explain the uneven temperature, and passed the problem back to Siemens. Siemens response was that neither material, nor manufacturing defect was evident, thus deemed the appliance was working as designed.

Could have tried another rear fan, or maybe tried replacing the rear circular heater element, but as a kitchen refurb was overdue, decided to replace the appliance with two single ovens. Thus the Siemens oven, whose interior is immaculate, is being offered for sale, collection only, and for a very low price bearing in mind the stated known problem.

(Note: weight is approx 42kg, thus reason for collection only by buyer)