Zanussi oven not heating up
there is usually a heating element to try to keep the ducts from icing up. If this becomes faulty, or if there is a very heavy load of ice (perhaps the door was left open, or has a bad seal, or a steamy stew was put in there with no lid) then the blockage would occur more often.
p.s. I once defrosted without pulling it out, there was so much water that it filled the evaporation dish and overflowed, when I saw that and pulled it out, water lurched out and got into the electrical starter and blew it up
luckily it was a plug-in part and easy to change myself.