Well, problem finally solved.
After much aggrevation, swapping all sorts of parts from one pump to another, it was suggested by the supplier (whom I finally got hold of) to try putting the inlet pipe directly into the "in" side of the pump.
When I did this it worked fine, which narrowed down where the problem could be. After much swapping and changing of pips and checking of the push fit conenctors, it came to light that it was a problem with the T connector.
If I slightly lifted the T piece up it caused the problem as described, as it must ever so slightly break the seal with the pipe. When it was pushed back down into place, all was ok....
Underneath the T piece in my pump box is the remote control black box, which can easily push the T piece up, so I moved this elsewhere.
So after all that it was a small part moving......
On one hand I am glad it's sorted, on the other hand I am annoyed I spent so much time trying to sort something that was so anoyingly simple in the end....
Thanks for all your help guys, hope this info is ok use to someone else at some point.
Cheers
Steve
