I have exactly the same problem with a 4 year old Neff K8525x3GB. The fault is due to a bad joint within the cold circuit behind the fridge wall (at about mid-way). This has caused the fridge wall to be 'expanded' to make a bulge into the cabinet, where a lot of ice now forms, the rest of the fridge being moist with water droplets, and the thermostat continually telling the fridge to cool down.
The fridge temperature even at maximum cool is about 12 degrees C.
The service engineer said he has met several Neff (and associated manufacture) models with this fault, and he stated that Neff no longer therefore has the quality control that they used to have.
Although the freezer section was keeping its temperature, in the last few days that temperature has risen - so the freezer is also unusable.
Unfortunately there is no repair possible - the whole thing is now just worthless.
I have removed some of the foam insulation from the back of the cabinet and found the place from where the coolant is leaking,so the service engineer was correct in his statement.
I have removed the kitchen cabinet where the fridge freezer was installed and I am about to purchase a free-standing model, as a new "built-in" Neff unit is about £1000!.
I cannot recommend Neff to anyone now.
Alan, August 2009
