wiring Honeywell CMT927/CM67 RF

If anyone could point me in the right direstion here I'd be really grateful...

I've just bought a Honeywell CMT927 wireless programmable room thermostat which I think is the new version of the CM67 RF. It's to replace a simple mechanical dial thermostat which has four wires attached, earth two neutrals and a live. This shows a wiring diagram for that one:

http://content.honeywell.com/uk/homes/Catalogue/Heating Controls/2.17 T6360.pdf

It looks like the 927 needs power all the time to work its wireless receiver so I think needs a separate live and neutral for that.

There are another four wires sticking out of my wall now behind the mechanical thermostat so I'm thinking one of them will be a live that I can use to power the 927 and probably one a neutral. Have ordered a voltage tester from ebay to make sure what they actually are.

There is a wiring diagram here:


http://europe.hbc.honeywell.com/netherlands/productcatalogue/pdf/en0h8556uk07r1006.pdf

If anyone thinks I'm way off course with this or maybe even on the right track lol any comments would be really welcome as I don't normally attempt things like this! Thanks

I might be wrong but it sounds to me like you want to replace the thermostat with the receiver unit and use some or all of the existing wiring to connect it up - is this right?

Assuming that it is, I would not do this under any circumstances. The effect would be to continually power the receiver on and off with timed demands for heating which it is not designed to do. The Honeywell unit is a simple zero voltage relay and should replace the central heating function of whatever programmer you are currently using. It should be located near to the existing wiring centre.

From the instructions you can see that it requires a permanent live and neutral connection. If you have a 3-port motorised valve then you should also connect live to port 'A' and connect port 'B' to the white wire in your wiring centre. If you have an two 2-port valves, then port 'B' should be connected to the brown wire of the heating zone valve.

In both cases, you should identify the heating connection from your programmer, disconnect and make safe. You should also identify and isolate all wires that are connected to your existing room thermostat.

I hope this is not a replacement for the CM67, that, or I hope the link pdf is wrong, since it doesn't have the easy profile setting of the CM67.

Thanks EliteHeat, I see how it can be done now, I'll have a look at the wires on the old programmer later today.

jonn.y said:

Thanks EliteHeat, I see how it can be done now, I'll have a look at the wires on the old programmer later today.

Click to expand...

Remember that the wiring will look quite different due to the fact that you are combining a thermostat and effectively a programmer in a two-wire operation.

This is what I'm attaching it to, there's a wiring diagram on p22, looks ok I think:

http://www.gledhill.net/water-storage/downloads/technical-manuals/boilermatemain.pdf

Thanks again

(This is where I saw the CM67 RF was being replaced, oilman)

http://www.heatingcontrolsonline.co.uk/product_info.php?cPath=21_31&products_id=68