Locate the pressure switch - a round item about 3 inches across. Its an air operated switch which tells the machine water has reached the correct level. Disconnect the rubber pipe from the switch and blow down through it to clear any blockage. Switch itself may be faulty.
Check the filter unit for blockages.
Disconnect pump from sump hose and check for obstruction in either item.
check out www.2ndwave.co.uk/manual for more info.
dan
January 2008