I had the same problem. I read on another website that, although this is caused by the pressure switch, often it does not need replacing, there is a reset procedure that they don't tell you about in the instruction book. First, check all the hoses are OK and not kinked. Clean out the filter behind the front bottom panel, just in case. Then, switch on the power, set a program, and press AND HOLD the start button for 30 seconds. This worked for my machine!
Spyke Golding, September 2007