Hi Andy. I've done mine today. It's worked so you may wish to give it a try. I'm only a nosey DIY'er.
As always follow basic safety rules including unpluging the washer.
Remove top from washer (2 screws at the back, lift backwards and upwards from rear edge)
Lift air pressure switch (the round plastic bit with a small plastic tube attached to the bottom of it. )
off right hand side panel. Move bottom of switch towards drum and lift.
Remove tube (twist and pull)
Blow down the tube till you hear water bubbling (a drinking straw served as a usefull extension)
Blow gently into the air pressure switch (you should hear the switch operate). blow a bit harder till you hear the switch operate. I did this several times. (if you don't hear it click even though you are turning blue, you may need a new switch???) Reconnect tube to switch.
Remove and reconnect the electrical connection to the switch.
Refit switch to side panel & top to washer.
Run on a rinse setting (to remove anything you have dislodged).
Hope it helps, I've just told you what worked for me. No guarantee. BE SAFE. A qualified engineer is cheap compared to !!!!!!!!!!!!!
Keith, October 2008