Yes you can, its probably what i would do.Could I not just replace the T in the 15mm pipe with an elbow to take the return straight back down? Then bring the cold water feed round and T into the horizontal pipe below the pump? Any chances of a pic of the H layout?
Also the 15mm return from the cylinder - will that be a problem or is that fine to be like that?[/quote]
Thats fine, quite normal to find 15mm return from cylinder. It restricts the flow in a similar way to how a balancing vlave would