I have a Zanussi ZNB 323 fridge freezer. I have a problem were ice is building up in the compatment in the freezer were the fan is located. Not sure what is causing this as the fan is operating and the fridge seems to be defrosting ok. If I remove the ice it is ok for a few weeks and then it has built up again.
Most likely the defrost cycle is not operating correctly. Heater most likely gone, you’ll need to dismantle & check if its open circuit, it is not the easiest to access.