Thanks guys for all the advise. I've just realised that in addition to
fitting the anti-graivity loop, if I want to place the pump above the
hot water cylinder then I need to use an essex flange which means
drilling a hole in the side of the cylinder. I'm not too keen on this
and thought I could just replace the existing top fitting with a Surrey
flange. I may have to look at other options first, most obvious at the
moment is to put the pump under the floorboards, but I'm a little
concerned about noise and vibration.