Installation of CM900 to Bosch 28cdi

[RADARONTOP]

Hi,

Tearing my hair out here over something probably very simple! I currently have a Worcester Bosch 28cdi combi boiler which has no remote thermostat. I therefore purchased the Honeywell CM927/921 wireless thermostat. Has anyone had any experience of fitting this?
Do I just remove the current control unit and wire in the Receiver box? The current control unit only has three wires connected to it from the boiler but the Honeywell receiver says it requires 4? I'm a bit of a biff when it comes to electrics but thought this would be fairly simple!

Any advice, greatly appreciated!

 

[clf-gas]

Volt free connections on boiler, power to reciever, volt free to boiler terminals.

 

[RADARONTOP]

That's still over my head! I think I'm certainly a step by step person. On the Receiver I have ; N,L,L,A,B,C,D,E
On the boiler there is the Red,Green,Blue.
Receiver instructions say N - N, L - L2, T1 - A, T2 - B.
Thanks

 

[clf-gas]

Which model boiler do you have exactly, is it the older mark II or the newer greenstar.

 

[RADARONTOP]

Just looked at the boiler, all it is says is 28CDI RSF Combi. I think it's about 6 years old but I've only been in the house a year.
Just don't want to try anything without some good advice incase I blow something.
Cheers.

 

[clf-gas]

Right, thats the older boiler, discontinued about 2 years ago.

Very easy job to do then, so to make it easier for you Heres the Honeywell Thermostat wizard, follow it step by step.

http://yourhome.honeywell.com/Consumer/Cultures/en-US/Support/Thermostat+Wizard/


Ill run through it now with your stat details, you do the same

Sorry that was the wrong link, thats the link

 

[RADARONTOP]

Thanks mate, that looks ideal but it doesn't seem to list the CM921! I got it off ebay so i'm not sure how old a model it is.

 

[clf-gas]

Basically take L&N from boiler to reciever, from reciever take T1 and T2 to boiler Ls and Lr, there will be a link in these terminals on boiler.

 

[D_Hailsham]

That's still over my head! I think I'm certainly a step by step person. On the Receiver I have ; N,L,L,A,B,C,D,E
On the boiler there is the Red,Green,Blue.
Receiver instructions say N - N, L - L2, T1 - A, T2 - B.

The receiver instructions are very general as they have to cover all boilers. You will not find any terminals on your boiler labelled T1 or T2.

Presumably your existing controller is just a timer. If so this can be left in place and just set to run continuously.

Inside the boiler there is a terminal block with three terminals labelled Ns, Ls and Lr. It's next to the mains connection. You need to run a three core cable from these terminals to the receiver - you may have to buy a three core plus earth and ignore the earth wire, do not be tempted to use a two core plus earth.

1. Turn off power to boiler.
2. Remove link between Ls and Lr (Thanks for the reminder clf-gas!)
3. Connect the red core to the Ls terminal, blue to Ns and the third core to Lr

At the receiver.

4. Connect the blue core to N, red core to L and third core to B.

5 Using a piece of short length of wire, link either L terminal to the A terminal.

Job done. Switch the power ON.

Hint!

Before fixing the receiver in place you should check that you get good reception from the proposed control unit location. The easiest way to do this is to connect a length of two core cable to the receiver L and N terminals and the other end to a three pin plug. Plug this into the mains and follow the Installation Manual instructions on "RF Communication Check (Test Mode).

 

[bengasman]

just take the manual of your boiler and compare with the manual of the stat, and it will be crystal clear.
make sure you safely disconnect the current timer, presumably the dark grey wb-unit.

 

[RADARONTOP]

Thanks for the help guys, it appears to be working well. I've just left the old timer intact and it doesn't seem to be having an effect on the new thermostat operation