We had this problem. I trawled the internet and found all sorts of answers, most of which involved getting rid of the machine, however, I found one which said do not put the pans on the bottom rack. So we gave the whole machine and filter a good clean out and did not put any pans in, hey presto it works every time now, may not work for you but worked for us, Hope of some use
Bigdaz, July 2007