Connecting CM67 thermostat to 38cxi Glowworm combi

[Dean Lawrence]

I have a Glow-worm 38cxi combi boiler (very happy with it by the way) and I've decided to install a programmable thermostat. The one I've decided on is the CM67 RF NG, not least because of the good reports it gets on this group.

Now, the installation guide for the CM67 relay (HC60NG) is a bit sparse. Basically the mains wiring is OK, but it shows 2 wires leaving the relay going to a symbol which I take to mean the boiler to 2 switches marked T1 and T2 as follows...

HC60 A B C D E | | BOILER T1 T2

But on the diagram there is a little picture showing switching between A and B and A and C...

HC60 |------------| | / \ A B C

So T1 on the boiler A can be connected to B or C either of which is directed to T2 on the boiler.

This text is also printed on the picture...

24-230V A-B:10(3)A 0..30 deg C /

[dean]

I think I may have found the answer to this. The HC60 is voltage free and so it can just be connected to the votlage free controls terminal on the combi. No problem their but I do have another question.

Do I need to make the connection between A and C terminals within the HC60 myself (ie by adding a piece of wire between them)?

The reason I ask is because the diagram on the application guide shows just such a connection, but the accompanying text says "just connect terminal A and B to two boiler terminals and the job is done", which implies there is no need to manually make the A-C connection.

If this doesn't make sense, here is a l> I have a Glow-worm 38cxi combi boiler (very happy with it by the way) and

[Set Square]

The stat has change-over contacts - because it can be used for heating *or* cooling. You're just using it as a switch - so you only need to use 2 of the

3 contacts - common and normally closed. The boiler will then run when the room temperature is below the stat setting, and will switch off when the room gets up to termperature, and the stat operates.

Hope that makes sense!

[dean]

[Set Square]

There *isn't* a link between A and C. What the diagram shows is the

*internal* workings of the thermostat switch. When the room temperature is low, A is connected to B - so the boiler runs. When the room temperature is high (above the stat setting) the contacts change over and A is connected to C instead. Forget about C - that is only needed if you use the stat to drive an air conditioner - so you need it to come *on* when the temperature is high. For your purposes, just think of it as a switch between A and B which is ON when it's cold and OFF when it's hot.

Does that make any more sense?

[dean]

Ahh! Yes, that makes perfect sense. The diagram is a representation of the thermostat switching in response to the temperature (what you buy one for really). Yes, I understand now. Thank you very much for your help. All I need to do is connect the two wires from terminals A and B on the HC60 to the voltage free terminals on the boiler and away it will go.

D> There *isn't* a link between A and C. What the diagram shows is the

[Set Square]

Glad to be of help!

One other thing - *please* post your replies *below* the message you're replying to - *never* above!