In an earlier contribution to this discussion,
Jon Connell wrote:

On 12 Dec, 15:29, "Roger Mills" wrote:
Is it a combi boiler which produces 'instantaneous' hot water, or do
you have a hot water cylinder.

It's a combi.

What reading is shown on the sealed system's pressure gauge?

A little over 1 bar.

Jon

In that case I'd tend to suspect either the pump or the diverter valve in
the boiler.
--
Cheers,
Roger
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