Baxi Duo Tec boiler and Nest thermostat connection

[Sargro]

Hello,

I am trying to figure out how to connect the Nest and HeatLink to my condensing boiler - Baxi Duo Tec Compact+ 20 GA. It is a new set up, so no previous thermostat connection, and I do not have the Nest at hand - trying to figure out what I need and what is possible, before buying anything.

Picture 1 - user manual on thermostat connection
Picture 2 and 3 - the terminal box on my Baxi
Picture 4 - service manual found on Baxi website


So as I understand, I would need to connect Terminal 1 and 2 to the HeatLink, and here is where I have some questions:

1. Which terminal should connect to which connection in the HeatLink? Manual that I have, and the one on Baxi website seems to show terminal 1 and 2 in different positions.
2. As I understand, Heatlink would still need external Live and Neutral wires for power supply, correct? Or could I power it using the L and N terminal in the boiler?

Thanks

 

[stem]

There are different ways of connecting Heatlink's to boilers hence the appearance of what often appears to be contradictory information. Also boiler manufacturers modify their products from time to time, so it's important to use the information supplied with your boiler and not supplied by Google.

If I were adding a Nest to your boiler, I would remove the link between boiler terminals 1 & 2, shown by the 'X'

Then connect these terminals to Heatlink 2 (Heating common) and Heatlink 3 (Heating call for heat). It doesn't matter which way around they go, it's just a switch. Under no circumstances add any additional wires to any of these terminals. They are "low voltage" and would not appreciate being connected to the 230V mains.

Then add a permanent N, L & E mains Supply to the Heatlink to provide it with power. This should be connected to the same 3A supply as your boiler, so that the same switch isolates the Nest and the Boiler.

 

[Sargro]

thank you Stem, this solves a couple of headaches.

I have a couple of other "stupid" questions.
Now, would running extra wires form L and N boiler terminals (adding wires to what is already there) to the Heatlink, would make sense? It would be safer to do as you suggested and just run new mains from the same supply, right?
And by not adding any additional wires, you have the Heatlink in mind, correct? As it looks like boiler terminals 1 and 2 are giving out 230v, no issues with connecting that to the indicated Heatlink terminals, correct?
It seems that stranded wires does not work with Nest, so when connecting Heatlink to the boiler, should I also use solid copper wires?

 

[stem]

Now, would running extra wires form L and N boiler terminals (adding wires to what is already there) to the Heatlink, would make sense? It would be safer to do as you suggested and just run new mains from the same supply, right?

It's the same thing. If you connect the Heatlink N,L & E to the boilers 230V supply terminals, by default, here in the UK you would be connecting it to the same 3A supply, and that's how it's normally done. Maybe it's different in Lithuania, if you don't use fused connection units.

it looks like boiler terminals 1 and 2 are giving out 230v,

The manual you have posted doesn't state the voltage it just says "low voltage".

Generally in boiler speak, 'low voltage' is used to refer to something in the region of 20 to 24v. However, it doesn't really matter because Heatlink terminals 2 & 3 are just a volt free switch that will join the wires connected to the boiler terminals 1 & 2 together when 'on'. [Which is what the yellow link is doing now] So, it will switch whatever voltage is applied to it. But the instructions for connecting it remain the same. Boiler terminals 1 & 2 connect to Heatlink 2 & 3. Don't connect anything else.

It seems that stranded wires does not work with Nest, so when connecting Heatlink to the boiler, should I also use solid copper wires?

Stranded, solid or a combination of the two will be fine, as long as they are suitably rated and properly installed. I'm not sure how you came to that conclusion.

 

[Sargro]

The snip that you give is referencing to the Terminal Block M2, where some proprietary Baxi remote control could be connected, while the thermostat should be connected to the block M1, and that is rated 230v. But if it doesn't really matter, then I guess all good. And I did see some similar topics with very similar boilers and pretty much exactly the same terminal blocks, where everything was working fine.

As for the stranded wires, Nest website states that it will not work with high OR low voltage systems with stranded wires. Over here. But I guess it only refers to the Nest itself.

In any case, thank you for your help! Will go ahead and order the Nest now.

 

[stem]

OK, we don't have the stranded wire prohibition in the UK, so use both types of wire. Things must be different in Lithuania, so go with your local requirements.

Regarding the connections, if these are the terminals 1 & 2 that you are referring to, in the bottom right in the diagram:

and they are the same as in this photo with the yellow link:

then I believe that's fine, and it can be wired as we have been discussing. The terminals to the left can provide you with the 230V for the power supply to the Heatlink.

Having said that, this assumes that the version of the Heatlink that you have is the same as the one we get in the UK. I'm puzzled by, some of the comments in the local Nest manual you have posted.

"Stranded wires may indicate that your heating and cooling system uses high voltage (line voltage). The Nest Thermostat is not compatible with high voltage systems OR with low voltage system that use stranded wires."

Here we can use the switching terminals 2 & 3 with 24v or 230V as they are voltage free. Probably best to get it checked out locally just to make sure.

 

[Sargro]

So I did some more digging, and it seems that the stranded wire and low voltage requirement is only for US, as they do not use the Heatlink. The Nest manual that I linked to was not local, it's for US, so my bad, sorry for that. And I will be purchasing UK version in any case, so I do think it will be fine. Thank you for your help again

 

[stem]

Like I said before:

it's important to use the information supplied with your boiler and not supplied by Google.

It's caught you out twice now

 

[Kestutis7]

Hi, I have almost the same case (Nest thermostat + Baxi Nuvola platinum) and I have one additional question. By connecting the wires you did connected the nest via on/off method or Opentherm? I am interested to connect my baxi boiler via opentherm protocol and need some help with that.

Thank you in advance!