adding RF thermostat to CH

[DW]

On advice I've just purchased a a Drayton RF3 wireless room thermostat for my CH system that was previously controlled by radiator TRVs and timed by a Tempus Seven Programmer.

I'm not sure if

1. the Drayton RF3 should totally replace the programmer and be left to control HW and CH.

1. Or should I leave the programmer to control the HW and put the thermostat in series with the programmer for the CH and just leave it on the ON position so that the room thermostat controls the CH.

I think option 2 makes sense?

How would this be wired in?

Many Thanks

[DW]

[Set Square]

Definitely Option 2 - it makes no sense for the room stat to control the hot water!

From the pictures in your other post, it's pretty clear that you've got an S-Plan system - with separate 2-port valves for CH and HW. The the CH side of the programmer currently controls the CH valve , and the HW side controls the HW valve. The secondary contacts on both valves turn on the boiler and pump whenever either valve is open.

So the CH feed from the programmer needs to go to the programmable stat and then on to the valve motor - rather than going directly to the motor, as at present. On the orginal programmer, leave CH on constant and do the *actual* timing with the programmable stat.

The HW side of the original programmer will continue to control the hot water. Have you got a cylinder stat? If not, you *should* have one in series with the feed to the HW valve's motor.

See S-Plan in

[DW]

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:

looks like I will just need to wire in the SCR Receiver to the Live (Brown) and Neutral (Blue) 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?

[Set Square]

It looks like I will just need to wire in the SCR Receiver to the

Yes

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 ______ Please reply to newsgroup. Reply address is invalid.