Zanussi ZX99 intelliset fault?

We have a ZX99 that has been reliable for 4 years.
Recently it had started beeping. A power-off reset would clear the alarms for a few hours and then they would come back.
I got an electronic thermometer and the fridge was at +7C and the freezer at -2C. I took the cover off the lower back and cleaned there and the vents at the front. I turned both dials down to min.
For 12 hrs the temperature didn't change from the above but then (with nothing being touched) it went to -1C for the fridge and -10C for the freezer within the next 12 hrs.
I turned the fridge up slightly and it went to 0C but the freezer went up to -2C but it wasn't touched. This took 4 hrs.

Is it the compressor, one of the thermostats, switches, control panel or anything else. It has me baffled.