In an earlier contribution to this discussion,
DW wrote:


Thanks Set Square.
Yes I do have a cylinder thermostat but not really sure how its wired
in.... goes into wiring box pictured anyway.
So looking at the wiring diagram pictured for the thermostat I've
ordered:

http://www.invensyscontrolseurope.co...tat3i_RF3i.pdf
It looks like I will just need to wire in the SCR Receiver to the
Live (Brown) and Neutral (Blue)
Yes

and then what for 1, 2, 3? What
colours should common, heat satisfied and call for heat be? I presume
I don't need to change any of the wiring to the CH 2 port valve?

You need to find the wire which goes from the CH ON connection in the
original programmer to the motor live connnection in the CH 2-port valve
(probably brown - but you'll have to find the *right* brown wire by tracing
it. In effect, you need to cut this wire in half and connect one of the cut
ends to 1 (common) in the SCR receiver and the other cut end to 3 (call for
heat). Don't connect anything to 2 (demand satisfied) - that's only needed
in special cases, or for switching cooling rather than heating equipment.

Provided the volt-free contacts in your motorised valves are connected as
per the S-Plan diagram in the Honeywell reference which I cited earlier,
boiler and pump control will take care of themselves once you have put you
new stat in series with the motor feed.

One other thing which I should have said last time: If you've got TRVs on
all your rads, you need to disable the one on the radiator nearest to your
new room stat - otherwise the TRV could turn the rad off before the room
stat gets a chance to work. Simply removing the thermostatic head off the
valve will do.
--
Cheers,
Set Square
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