help - wiring programmer

[jackfoley]

Hi all,

I have just purchased a honeywell cmt927 thermo to wire into my combi boiler (Worcester 28si).

The diagram in the instructions show the live feed to the boiler mains linked from the receiver rather than the spur (unlike the neutral which feeds the boiler separately).

Is this correct? I would have though the boiler mains live feed would have been separate from the receiver.

 

[D_Hailsham]

The diagram in the instructions show the live feed to the boiler mains linked from the receiver rather than the spur (unlike the neutral which feeds the boiler separately).

Is this correct? I would have though the boiler mains live feed would have been separate from the receiver.

Both boiler and the CM927 receiver require a permanent supply, so it does not matter which comes first.

If your supply goes to the boiler, then all you need to do is run a three core plus earth heat resistant cable (0.75mm Tower brand from B&Q) from the boiler to the receiver location. Connect as follows:

Boiler L to Receiver L
Boiler N to Receiver N
Boiler Lr to Receiver B
Link L to A at the receiver.

The earth wire is not used so it should be made safe at both ends (cut back to outer sheath).

PS Make sure that you have good communication between the two parts of the CM927 before fixing the receiver to the wall.The easiest way to do this is to attach a long lead with a 3 pin plu on one end to the receiver L and N terminals and follow the instructions in the CM927 book.

 

[jackfoley]

Many Thanks D.

The next question I have relates to the wire size.

Currently I have a 10mm wire going into the current timeswitch. The new one only takes 7mm.

Can I connect the existing 10mm wire to a piece of 7mm wire via connector block in the backbox or is this dangerous. If I can do this it would save me from replacing the existing wire to the boiler which runs through a hole in a cavity wall...

 

[D_Hailsham]

Can I connect the existing 10mm wire to a piece of 7mm wire via connector block in the backbox or is this dangerous.

That will be OK.

 

[simond]

What timeswitch?

I thought you were adding a CM927 to a combi. No mention of a timeswitch.

The CM927 only has small cable apertures, however, you can excavate a piece of plaster and run your 10mm diameter wire behind the receiver and go through the big hole in the back.

If your wiring is 'flush' and you have 1.5mm conductors, these are a struggle to fit into a CM927 but possible. You could fit a connector block in the flush box if your wiring has one.

But your description is too vague.

It isn't necessary to power up CM for radio recep before use, the thing can just be fitted and used. Make sure you go in the Eng menu and turn on Optimisation (level 8, set value from 0 to 1).

 

[jackfoley]

thanks.

Which wire should i buy? Is 0.75mm still too big for this receiver?

 

[D_Hailsham]

Which wire should i buy? Is 0.75mm still too big for this receiver?

That's what I used.

It isn't necessary to power up CM for radio recep before use, the thing can just be fitted and used.

I agree it is not necessary; but there is nothing worse than fixing the receiver to the wall and then finding out that you cannot get a good signal from the proposed location of the controller.

 

[jackfoley]

hi again, when you say link L do you mean Ls on the boiler?

 

[D_Hailsham]

hi again, when you say link L do you mean Ls on the boiler?

NO! Read what I said: Link L to A at the receiver.

Ls on the boiler is not used.