Wiring Honeywell CM927 to Worcester 28Cdi

[SteveZodiac]

I'm replacing a Honeywell ST6100C timer with a Honeywell CM927 programmable thermostat to a Worcester 28Cdi. Can someone please advise on the correct wiring, as the wiring diagrams in the installation instructions and on the reciever box seem to conflict on which live terminal to use on the receiver box.

Boiler has:
Neutral, Live, Live (switched)

CM927 receiver box has:
Neutral, Live 1, Live 2, A, B, C, D, E

First, which live do you use on the receiver box, Live 1 or Live 2?. The instructions diagram suggest Live 2, but the box diagram suggests Live 1.

Second, since I've only got 3 terminals on the boiler I have to link two terminals on the receiver box. I'm assuming that C on the receiver is OFF and B is ON, therefore I need to link the Live terminal (1 or 2 though?) and B terminals on the receiver. Is that right?

Thanks in advance.

 

[Statia]

The CM927's relay box requires two lives. One is to power the relay/receiver itself, the other is the live which when switched, switches on the heating.

In mine, I split the live into two with a terminal block with the existing live going in one side, two cables coming out of the other.

1st live goes to L
2nd live goes to A
Neutral goes to N
Switched live (to boiler) goes to B

You shouldn't need to touch any boiler wiring. Just wire in the new thermostat in place of the old one.

It's less complicated than you think

Untitled

• Statia
• 26 Nov 2008
• 1

 

[D_Hailsham]

I'm replacing a Honeywell ST6100C timer with a Honeywell CM927 programmable thermostat to a Worcester 28Cdi.

Don't you have a thermostat or have you just forgotten to mention it?

Boiler has:
Neutral, Live, Live (switched)

CM927 receiver box has:
Neutral, Live 1, Live 2, A, B, C, D, E

It does not matter which Live terminals you use on the receiver, they are linked together.

Connect one L terminal and the Neutral to the Ls and Ns terminals on the boiler.
Link one L terminal on the receiver to the A terminal with a short length of wire,
Connect the B terminal of the receiver to the Switched Live (Lr) on the boiler.

 

[SteveZodiac]

Many thanks for the prompt replies both of you.

In mine, I split the live into two with a terminal block with the existing live going in one side, two cables coming out of the other.

1st live goes to L
2nd live goes to A
Neutral goes to N
Switched live (to boiler) goes to B

You shouldn't need to touch any boiler wiring. Just wire in the new thermostat in place of the old one.

I presume you mean you split the live instead of linking any terminals on the box. And I need to follow diagram 4a instead of 4b which did cross my mind!

Don't you have a thermostat or have you just forgotten to mention it?

Hard to believe I know, but I haven't. Putting it right now though!

It does not matter which Live terminals you use on the receiver, they are linked together.

Connect one L terminal and the Neutral to the Ls and Ns terminals on the boiler.
Link one L terminal on the receiver to the A terminal with a short length of wire,
Connect the B terminal of the receiver to the Switched Live (Lr) on the boiler.

Yes, it occurred to me after I posted that the live and A should be linked.

 

[Statia]

I presume you mean you split the live instead of linking any terminals on the box.

Correct, you can do it either way. They both achieve the same result. It also depents on what gauge of wire you use as the teminals in the relay unit are tiny and it can be a squeeze to get two wires in one terminal.

 

[Statia]

Contradicting my own reply, if both live terminals are linked, you could use the other (unused) terminal to make the link