Try these solutions in these order:
1. Switch off the fridge and leave the door open overnight. Switch it back on in the morning.
Explanation: The sensor inside the fridge gets frozen and cannot control the temperature properly.
2. Switch off the fridge. Unplug it. At the back of the fridge (behind the unit, not inside) there is a large grid. Clean it with a hoover thoroughly. Open the fridge. Dry the back of the fridge if wet (inside the fridge). If frosted wait for it to defrost and then dry it. Plug in the fridge. Switch the fridge back on. This one worked for me.
Explanation: The dust in the grid deprives the fridge from cooling down and the unit can't control the temperature in the fridge section.
3. Switch off the fridge. -Unplug it. Empty it. Turn it upside down. Plug it in. Switch it on for 24 hours. Switch it off. Unplug, return to normal and switch on.
Explanation: This has to do with the pressure of the gas inside the compressor. I have not tried it but this advice as given to me by a qualified electrician when I commented the (in)famous F2 problem in Liebherr fridge/freezers.
Hope it helps. Regards. Albert