In an earlier contribution to this discussion,
Pete wrote:

Are you *sure* it is a gravity system?


Just come down from the loft. It is definatly a gravity system.


How does looking in the loft prove that it's a gravity system? I wonder
whether we mean the same thing by "gravity system".

I am talking about gravity (or natural convection) circulation within the
*primary* hot water circuit. If this is what you have, you will probably
have *four* water pipes connected to your boiler - 2 large (28mm) ones which
go to the indirect coil in the hot water cylinder, and two smaller ones
(22mm) for the central heating - with the pump being somewhere in that
smaller circuit - and with the primary flow in the HW circuit being
*unpumped*. Is that what you've got?

[I wonder whether you're defining "gravity system" in terms of having a
large header tank for the hot water system - so that hot water flows by
gravity (rather than by mains pressure) to the hot taps. If this is the
case, we could be at cross-purposes, and may need to start again!]
--
Cheers,
Set Square
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