Fitting Honeywell cmt927 thermostat to Baxi DuoTec 40HE

[m4rky]

Hi,

We have had a Towerstat RF/BMs but we are now on our third one in two years as they keep failing in October!?!?!?.

I have had enough of them and have decided to fit a Honeywell CMT927 wireless thermostat to our Baxi Duo-Tec 40HE-A.

I am after a bit of advice on how to wire the receiver to the boiler.

Thanks,

Mark

 

[mikely]

The connections at the Towerstat receiver are:
1 – Neutral input
2 – Live input
3 – Common input
4 – Normally open output

On the 927 receiver, using the wires from above, connect:

1 to N
2 to L
3 to A
4 to B

 

[m4rky]

Thanks for your reply mikely but the original Towerstat receiver is not wired into the boiler. Its the plug-in one that fits in the mechanical clock slot (which is the main reason I bought the towerstat as no wiring was required).

The boiler instructions shows the following schematics:

View media item 38873
View media item 38874

 

[mikely]

So you need wires from L and N at the boiler terminals to L and N of the receiver and then connect A and B at the receiver to terminals 1 and 2 at the boiler, as per the upper figure 'Room Stat' connection. An alternative is that you can take the L and N from the Switch fuse unit that supplies the boiler, as per the lower diagram.

It doesn't state it in the bolier manual, but the connections into the boiler should be made using heat resistant cable.

 

[m4rky]

Cheers. I hoped it would be that simple.

 

[m4rky]

As I mentioned in the first post, we have a Towerstat plug-in wireless receiver that fits in the mechanical timer slot of the boiler.

When I take this out and wire in the Honeywell what do I do with the wires that did go into the old Towerstat plug-in receiver?

Also there will be no cover of the slot so you will be able to see/touch the plug-in module wires inside? Can I just tape them up?

 

[TonyRick56]

Glad to be rid of the Towerstat I fitted a couple of years ago, even though the RX did fit nicely into the circular port. I've left the front of the Towerstat in place as a blanking plug, and used a thick plastic strip as a cable clamp to hold the cables coming from a four-gang connector.
I don't know if I've missed something, but when I ran the test as in the Installation Manual, I got a link ok, but the boiler wouldn't fire up. I tried the button on the RX next to the indicator lights, and everything worked fine. I don't think this is in the Manual.
Thanks to M4rky for the wiring help.