we had this problem. we followed the instructions in the manual to check the drain filter. We didn't find anything. The called the service man - he got down, removed the drain filter and shone a torch to the pump beyond, and found a rubber band had got past the drain filter, he pulled it out with pointed plyers. He said it was a common problem, also hair clips get down there. Anyway, problem is fixed. So try that.
rebecca, July 2008
