Miele KFN12923 fridge freezer – erratic fridge temperature.

Hi All, problems with the Miele FF again…. Freezer is working fine, with no ice build-up on the condencer, but fridge temperature is all over the place: sometimes the correct temperature e.g. 2 degrees C, but more often in the 5-8 degree C range. I don’t think it’s simply the door being opened too often. Rear panel is sometimes cold with a little frost, other times not at all.