I had the same problem after I forgot to empty the water. I did the following and it worked, but no promises:
Pull the tumble dryer out, remove the plastic panel on from the bottom right corner on the back to get to the float, empty any condensation out of the floats vessel (was only a few ml, not enough to have pushed the float up but as this was the only visible possibility maybe this wasn't helping things?), pull the float back down, and put everything back together.
Shouldn't have to do this in my opinion, but hope it helps.
Beth Fenn, November 2007
