In an earlier contribution to this discussion,
Keefiedee wrote:

On Oct 14, 2:14 pm, "PM" wrote:
Keefiedee wrote:
On Oct 13, 7:11 am, Keefiedee wrote:

I think I've got it. The pumps don't go between the thermostats and
the motorised valves, but are fed from the thermostats rather than
fed from the switches in the motorised valves.

Will someone please confirm?

Keith

Why do you want two pumps?

You have two valves which are opened /closed by the room stat and
tank stat. If either valve is open, the boiler fires and the pump
runs.

Because the HW and CH have separate pipework coming out of the boiler,
and the HW was only heated by gravity before I fitted the pump. I
know a pump isn't absolutely necessary, but I wanted a more efficient
system.

So what you have *isn't* an S-Plan system - because that would only have
*one* pump.

With two pumps, you don't actually need any motorised valves. You simply
control each pump with its (room or cylinder) stat - and you then need some
relay logic to fire up the boiler when either (or both) pump is running.
[You may then find that you still get gravity circulation in the HW circuit
when only the CH is supposed to be on - in which case a simple check valve,
which requires pump pressure to open it, needs to be inserted into the HW
circuit.]
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!