What is error number 4 on my Hoover AI130 washing machine?

you have a problem with your pressure switch - 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 that water has reached the correct level. If the filter was full of crud its likely the pressure switch pipe and the vessel it connects to are as well. Disconnect the thin rubber pipe from the switch and blow down through it to clear any blockage. If its badly bunged it may need to be disconnected from the drum and cleaned out. Switch itself may be faulty but its more likely the pipe is blocked. power off before starting any work.
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