I have a twin pump potterton boiler (it doesn't have a valve fitted to switch between HW/CH independently so I have to have the HW on to get CH) which is set to gravity feed, however although the control panel shows that the hot water is not on overnight, it is on all the time.
if your hot water side is fed of gravity this will always be on if your boiler is turnd on! as for 2 pumps i dont know why you need 2 because if your water is heated by gravity therfore not needing a pump. you shouldnt need 2 pumps for the heating side unless you live in a castle?
if you need any more info mail me
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