Drain machine by advancing to the empty part of program or running the outlet pipe into a bucket at floor level or run the outlet pipe out of the back door if it'll reach.
Check the pressure switch -the system that determines correct water level in the drum. Its a round item about 3 inches across with several wires connected, it sits under the top cover. Its an air operated switch which tells the machine water has reached the correct level. Disconnect the thin rubber pipe from the switch and blow down through it to clear any blockage. Switch itself may be faulty but its more likely the pressure pipe or the vessel attached to the other end of the pipe is blocked.
Also check the filter - generally located behind a panel at the foot of the machine.Some are obvious like little square hatches and some are hidden behind the trim panel at the foot of the machine. Once panel is removed the filter should be visible. Its generally a circular plastic fitting which unscrews in an anticlockwise direction.
Repair and service your own washing machine. Check out www.2ndwave.co.uk/manual.html
dannyboy
November 2008