On 10 Jan 2008 14:56:47 GMT, (Andrew
Gabriel) wrote:

Is there any advantage to splitting the house in two and having one
valve for upstairs CH and one for downstairs?

It can be. Depends on size of house and usage patterns,
and how long it takes to heat up and retain that heat.

Thanks for your reply. I see below that you have two zones. Can you
tell me more about your set-up and usage? What should I do to work out
whether I should do the same? I'm in a 1970's build so no modern-day
super insulation!

A 3-port is always open somewhere. It has a built-in switch
to signal the normall closed side being open. I believe there
are standard wiring diagrams for the different Plans on the
web.

The diagrams I found confused me! I hadn't appreciated the always open
aspect until you said. I assume the pump needs to switch on when
either thermostat calls for heat. Do you just run wires from both
'stats to the pump?

I think it's usually H/W on A and C/H on B. This is to fit in
with the standard wiring diagrams.

That's what the FAQ says IIRC but I whilst googling I found reference
that one manufacturer prefers you to use HW on B because this means
the valve is energised for a shorter period if I understand correctly.

downstairs is
heated more than upstairs, so the valve spends more time powered
off than powered up with the synchronous motor stalled.

Really? How does this work? You heat downstairs in the early evening
and then switch to heating the upstairs at night?

Thanks again.