Programmable thermostats

[dolby]

Hi, I have a Worcester 28i RSF combi boiler with a manual timer and a Danfoss room thermostat that is connected through 2 wires (I presume a live and neutral). My question is, can I simply replace the room thermostat with a 7 day programmable thermostat such as the Honeywell CM907 ? Would any additional wiring be necessary ? I presume if this is feasible then I would then just leave the manual timer on constant and just control it from the new timer.
Any help on this would be most welcome.
Thanks.

 

[fitz1]

the two wires are probably live in and switch live out.. i think its 240 volts.

 

[dolby]

Does that mean I could just replace the thermostat with a programmable one, and if so would I just leave the manual timer on constant ?

 

[fitz1]

as long as new programmer takes 240.

 

[dolby]

Cheers Fitz, thanks for the help. Do you know if the Honeywell CM907 would be suitable?

 

[fitz1]

not sure.

 

[D_Hailsham]

Do you know if the Honeywell CM907 would be suitable?

Yes, you can use a CM907.

The boiler has three terminals: Ns, Ls and Lr.

The existing thermostat will be connected to Ls and Lr - disconnect it.

You need to run a a 3-core cable from the boiler to the receiver. Connect red to Ls and receiver L; blue to Ns and receiver N; third wire to Nr and receiver B. Then put a link wire between receiver L and receiver A. You should use a proper three core cable - plus earth, if that's all you can get, but the earth is not used.

The existing timer should be put on constant.

 

[dolby]

Thanks for the help - all sounds simple enough.

 

[dolby]

Ok I have purchased a CM907 thermostat but the wiring is different from that suggested above. The boiler has 3 connections for the room thermostat marked
RN - Neutral,
RI - Switched Live
RL - Live
(The existing thermostat is connected to RI & RL)
and 3 connections for the existing manual programmer on the boiler itself marked
CN - Neutral
CI - switched live
CL - Live
The CM907 appears to have 3 connections - marked A, B & C, although C is blanked off and would only appear to be used in systems using Zone valves and electric actuators.
The suggested connections for a combi boiler show connection T1 on the boiler going to A on the receiver and T2 on the boiler going to B on the reciever.
Am I right in thinking T1 & T2 refer to Live and switched live?
In addition if I bridged the live and switched live connectors for the manual timer would I then be able to ignore this completely?
I tried to add the wiring diagram to this post but I am not sure how to do this.


[/list]

 

[dolby]

I have had a go at pasting the wiring diagram from the thermostat.

 

[D_Hailsham]

WB changed their terminal labelling and I was quoting the current ones.

You just need to connect RL to A and RI to B.

You could bridge the existing clock CI and CL terminals if you wanted to - then it won't matter if any one fiddles with the old clock.

 

[dolby]

Thanks again for the help.

 

[screech]

i think drayton do a programmable stat that only requires live and switch live. uses a couple of aa batteries so no need for the neutral and can be sited where your existing stat is with no extra wires or receivers added.

 

[dolby]

Sounds the same as the one I've got - a Honeywell CM907. Takes 2 x aa batteries

 

[DP]

Dolby, remove the room thermostat and fit Honeywell unit with wires connected to A and B. When new unit calls for heat, with old timer on constant, boiler should fire.

Easy as following off a log.

Warning. Switch power off. Also test both wires for mains voltage.

Personally, I would take the two wires to the boiler and scrap/ disconnect the timer all together