The main cause of this happening is that the self condensing pipe at the back of the machine has become blocked with fluff. You can get to this by removing the back panel. You will then see a plastic tube. You need to remove the pipe that connects to the bottom of it, then with an old wire coathanger poke it up the pipe and you should be able to get some of the fluff out. The more you can get out the better. I clean this section out of my machine once every 6 months, especially after the winter when i've been using the dryer more.
Louise
February 2007