Fixed the fridge... again... for now.

I'm getting seriously fed up with my fridge freezer. It cost us a lot of money and just outside of the warranty started icing up in the back until the ice built up around the fan and stopped it working. The engineer came out to have a look, told us we must have left the door open and defrosted it for us. Well even I can manage to defrost it. And I have... 4 times now in the last 2 years. As for leaving the door open - it has an alarm. Not possible.