In an earlier contribution to this discussion,
Keith G. Powell wrote:


This operation appears to be the same as my 1980s bungalow CH which
it is not a gravity system. It is fully pumped.


No according to the OP's description! He said that the pipes to the right of
the boiler - which are *not* in a pumped circuit - go to the heating coil in
the cylinder, and that the two zone valves are for two different heating
zones. He also said that he can't have CH without HW. All this is consistent
with a gravity HW system.

Of course, he *could* have got it wrong. The pipes on the right *could* just
go to the F&E tank, and the zone valves *could* be one for CH and one for
HW. But that is *not* how he described it.
--
Cheers,
Set Square
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