Installing wireless room stat into S Plan

[joncox]

I have an S Plan system with a Honeywell CM67 programmable room stat. When I installed the CM67 in 2004, I used two of the four wires coming from the wiring centre: red (live, A) and yellow (switch live, B). Blue (neutral) wasn't needed as the stat is powered from battery, and I taped this, along with the earth. All works perfectly.

However, the stat is poorly located and I'd like to upgrade to a CM927 wireless base unit and stat, with the base unit in the same place as the CM67 currently is.

Question: since the CM927 base unit requires power (N-L on wiring diagram from Honeywell website) as well as live and switch live (A-B), how do wire this? I have one live, but require two: can I bridge between the L and A terminals in the CM927?

Any advice gratefully received.

 

[simond]

You can't do this properly, I assume you have a three core flat cable with ECC.

However, you can do it improperly.

If you are going to run your existing 2 channel programmer with CH permanently 'ON' and use the CMT927 solely as your heating controller, then you could use the switched live from the HW/CH prog as the permanent live to power the CMT927 radio receiver. I would suggest the red wire.

Use the blue as the neutral, and link the red wire to terminal A on the switch inside the 927, there are two LL for this purpose.

Then use the yellow as the switched live to the motorised valve. If you want to be professional mark it with a brown tape or sleeve.


Of course, and I'm sure you have considered this, you could always just site the CMT927 receiver next to your wiring centre and wire it up conventionally, being radio it doesn't matter too much where it is sited. We are seeing better range out of the 927 than the CM67 model it replaced.

NB: You can't use the ECC to get you four cores, as I'm sure you know.

 

[gas4you]

Do as Simon says and install receiver unit next to wiring center. Problem solved.

 

[joncox]

Many thanks - very clear. Yes: the current CM67 is run in conjunction with a Honeywell ST6400C 2 channel programmer with the CH permanently 'on'.

Only issue with siting RF receiver unit next to wiring centre is that it would be in the airing cupboard, next to the HW tank, shower pump, CH pump, zone valves, programmer, etc etc.

The installation guide for the CM927 says it shouldn't be placed within 30cm of any metal objects - or within 1m of other electrical equipment - to avoid interference. I couldn't avoid this in the airing cupboard - any experience of whether the rest of the kit would interfere at all, or could I get away with it?

 

[D_Hailsham]

When I installed the CM67, I used two of the four wires coming from the wiring centre: red (live, A) and yellow (switch live, B). Blue (neutral) wasn't needed as the stat is powered from battery, and I taped this, along with the earth. All works perfectly.

So you have a 3 core (red, blue, yellow) + earth from the wiring centre to the existing CM67 position.

Question: since the CM927 base unit requires power (N-L on wiring diagram from Honeywell website) as well as live and switch live (A-B), how do wire this? I have one live, but require two: can I bridge between the L and A terminals in the CM927?

On the CM67 the L and A terminals are combined but on the wireless versions they are separate, so the programmer can be used with combi-boilers (see Diagram 4b) or sytems which use 24 (not 240) volt switching.

Use the Red and the Blue as the power from the wiring centre to the L and N terminals of the CM927 Receiver. Put a link (bridge) between the L and A terminals on the receiver as in Diagram 4a of the instructions. Use the Yellow as the switched feed back to the wiring centre. The Earth is unnecessary!

There is also an Application Note for S-plans with programable Stats on the Honeywell website at:

http://content.honeywell.com/uk/homes/files/pag110.pdf

It's for a wired-in type stat but may be helpful.

 

[joncox]

So you have a 3 core (red, blue, yellow) + earth from the wiring centre to the existing CM67 position.

Yes

On the CM67 the L and A terminals are combined but on the wireless versions they are separate, so the programmer can be used with combi-boilers (see Diagram 4b) or sytems which use 24 (not 240) volt switching.

Use the Red and the Blue as the power from the wiring centre to the L and N terminals of the CM927 Receiver. Put a link (bridge) between the L and A terminals on the receiver as in Diagram 4a of the instructions. Use the Yellow as the switched feed back to the wiring centre. The Earth is unnecessary!

Done, and tested: all works perfectly.

There is also an Application Note for S-plans with programmable Stats on the Honeywell website at:

Thanks for this - again very helpful