In an earlier contribution to this discussion,
Pete wrote:

"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Pete wrote:

Are you *sure* it is a gravity system?

99.9% sure. HW circuit is not pumped, only central heating - see
below.


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?

Not quite. I have TWO 28mm pipes going to the boiler. These 28mm
pipes form the HW flow and return.

From the 28mm flow there is a T piece and a 22mm pipe connecting to
the pump and then continuing to the CH flow.

CH return connects from a 22mm pipe to the 28mm Return via a T.

Is this still what you mean by gravity. - Would a diagram help?



I can picture it from your description without requiring a diagram.

It certainly sounds as if you have a gravity HW and pumped CH system - with
two independent circuits which share a bit of pipe close to the boiler
rather than being separately connected to the boiler.

If you go for a C-plan system, connect the pump as per the C-plan circuit
diagram rather than leaving it connected to the boiler.
--
Cheers,
Set Square
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