I have a double oven with hide and side door and I always clean them after use. I noticed a water mark going right down the middle of the glass from top to bottom. I contacted an oven cleaning person who refused to touch the Neff door because the removal of the door was too difficult so I had to get a Neff engineer out which cost £99 just to remove a water mark. I am always very careful cleaning the door but obviously this must be a bad design and in future I will have to be extremely careful so as to not use excess water that can drip down through a vent at the top of the door. Be careful when cleaning your oven doors!