How can I stop my washing machine overflowing?

Check the pressure switch - a round item about 3 inches across with several wires connected. 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 pipe is blocked.
Check out this site for spares : www.4directelectricals.co.uk
Check out this site for info: www.2ndwave.co.uk/manual.html

dan
February 2008