On Mon, 15 Dec 2003 17:11:27 -0000, "Set Square"
wrote:

What you need is, in effect, an S-Plan-Plus [see
http://content.honeywell.com/uk/homes/systems.htm] with 3 zones, 2 for
heating and one for hot water.

Use a standard programmer and cyl stat to control the zone valve for the hot
water - with 2 or 3 on/off periods per 24 hours, as desired - but always the
same temperature unless you manually twiddle the cyl stat (which is probably
acceptable). On the same standard programmer, set CH to permanently on and
use its CH ON contact to feed the programmable room stats. The actual on/off
periods (and different temperatures if desired) are then controlled by the
room stats - which in turn control their respective zone valves.

The volt-free contacts on all 3 zone valves are connected in parallel - with
the output side controlling the boiler and pump. That way, the boiler and
pump will run whenever one or more zones requires heat and will shut down
when they are all satisfied - achieving the desired interlock.

Very many thanks to all who responded.
My missing link was the need to still have a normal programmer to
handle the DHW - not realising that the programmable room stats do not
replace the programmer. I now have a fairly large bulge appearing on
my forehead!

I don't really have a problem running cables everywhere since the
whole place will be redecorated following the extension. I
I've had a look at the Danfoss site and can see that that would meet
the bill but have noted the comment from Christian concerning the
potential reliability of the RF stats. Since one may be 20m from its
receiver , I think it makes more sense to go the wire route.

Is there anything to choose in reliability of the electronics or TRV's
between various manufacturers?

Thanks again all

Ian