In an earlier contribution to this discussion,
ARWadsworth wrote:



I am sure that I have seen variations of the W plan for gravity HW
using a 2 port valve!

I think you're confusing it with C-Plan, which does that.

I doubt W plans will make a comeback. A W plan cannot meet part L of
the building regs as it does not allow total independant control of
the HW and CH circuits.

W-Plan is fully pumped with a diverter valve, and *does* provide independent
control and a boiler interlock, so I don't see why it wouldn't meet Part L.

If you actually mean C-Plan, that also provides independent control and
boiler interlock. It's actually devilish cunning in the way that it uses the
auxiliary change-over contacts in the single 2-port valve.
--
Cheers,
Roger
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