Switch off the power at the main switchbox!
Unscrew the cover
On the green valve you can line up the bit that moves to select power settings and remove it
Undo the two screws holding the outer switch frame and lift it off
Undo the two screws holding the valve body in.
Remove the valve body, underneath you will find an ordinary tap washer - probably split
Replace the washer - I didnt have an exact match but drilled the middle out of a large washer to match
Reassemble..
Pete, October 2011
