Freezer over freezes and ices up, and items on the bottom e.g. Potatoes will freeze. The "set temp " bottom does not respond for freezer compartment, but does for fridge compartment. I have switched it off, defrosted it, and left it open overnight in a warm room, but problem recurring. Temp showing -24C sometimes.
Brian Ford

Brian Ford, January 2016

Could be a failed thermistor / thermostat.

Also found this:

http://forums.moneysavingexpert.com/showthread.php?t=3294322

XXX, January 2016