It sounds as though your unit could be knackered as the symptoms you describe indicate that the ice has breached the insulation, but it could also be that the unit cant cope with the cold and damp in the room, try heating the room up for a day to see if it cures it or if it is a hotpoint and it has an economy switch on it switch it back to normal as I think that this controls the door seal heater.
powerhousesteve@hotmail.com, November 2005