Just a quick one.  I have a pump, it works and then stops.  I change the pump with my spare, it works it stops.  I then replace it back with the original, it works, it stops.  I replace it with the spare it works it stops.   What is going on.  Do I need to buy a thrid pump or is their dark magic at work.  Has anyone had similar problems, how long do pumps generally work for.  To they start and stop and how can i stop this issue as I leave home all in order and arrive at a customer and then bugger me it is not working.  Any advice welcome