Liebherr fridge stuck on 0 degrees

I have an (old) Liebherr fridge. According to the type plate it is KIB 2540 Index 20A/001 with service number 9981896-01. It has bio-fresh etc. The intruction book has the numbers 7081 080-01 on the front, but I am not what they mean

The fridge has suddenly started being too cold. In the morning it is now stuck at 0 degrees and one can here the fan whirring. We do usually have the "e" cool air circulation activated as recommended in the instruction book.

I am currently defrosting the fridge back to room temperature. I did notice that the drainage hole at the back of the lower shelf was blocked and have unblocked it.

Any other suggestions on how to cure this problem?

Thanks

Tudorfridge