After checking all the hoses and removing a 5p coin from the filter, I checked the valves and in the end removed the PCB (Look up from underneath, it's in the white plastic shielding where all the wires go). I found there was a short on 2 of the tracks. I removed the short by scraping between the tracks and then soldered a piece of wire to the 2 points that should have been connected and :- hey presto it works again.
Si, May 2006