We have a problem in that our Smeg Fr158 fridge keeps icing up at the back, producing large blocks of ice every few days. I assume the auto defrost is not working? Is that merely a replacement thermostat, the one inside at the back or is there some other cause.
Make sure the door is shutting/sealing properly, and the condenser fan underneath. If they’re ok then the fridge has system or compressor fault – its very unlikely to be the thermostat