Nest install on Baxi Comfort HT 330

23 Dec 2018
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Gentlrman, a little assistance please,
Installing NEST learning thermostat on Baxi hT 330 has external wall BAXI thermostat, connected to M2 boiler connections, 1&2.
Connected Nest, using lot voltage combi, heat link connected to mains, heat link 2 & 3 back to Boiler M2 connections 1&2. T1 and T2 back to thermostat. Green light on heat link, thermostat says connected. But no heat and no hot water.
The boiler came with add on accessory board M2 for original Baxi thermostat installation.
I am thinking that maybe I should go back to boiler M1 and connect M1 thermostat connection to heat link 2 and 3. I haven't tried this yet. I am afraid to just start trying different connections, don't want to fry something.
If any one can offer some assistance as to what the correct connections from boiler to nest heat link, it would be much appreciated.


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Hello Stan

I see you are in Italy so the products and methods you have may be different from what we have in the UK. However, I believe that your boiler is a combi and the wiring is as below:


In which case, there should be a permanent mains supply to the L and N, plus an earth connection. (In the UK this is from a 3A fused spur, but may be different in Italy)

I assume the yellow link shown between 1 & 2 above has been removed. The existing room thermostat should now be disconnected from the boiler and:

Nest (N) connects to boiler (N)
Nest (L) connects to boiler (L)
Nest (Earth) connects to boiler (Earth)
Nest (2) 'Heating Common' connects to boiler (2)
Nest (3) 'Heating call for Heat' connects to boiler (1)

You can then choose to power the Nest thermostat from a separate plug in power supply, or connecting it to Heat link terminals T1 & T2.

In the UK if it is necessary to open up a room sealed compartment to access the wiring terminals, this should only be done by suitably qualified and registered people. I don't know what regulations are in place in Italy.

If the boiler connections are different from above don't proceed.
Last edited:
Stem, I appreciate the assistance. Yes my boiler has the same connections. Yes it is a combi boiler, I also thought (M1) 1&2 to (Nest) 2&3 was probably correct.
I do have one other question. The M2 connection on my boiler, which was an add-on accessory in order to have the Baxi thermostat installed away from the boiler.
Just wondering, now I am connecting to the M1 thermostat connection, do I need to remove the M2 add-on connection? With it still connected to the PCB, do you think it will interfere or cause conflicts since I am connecting to M1 now? Also in the manual, when I see a thermostat connected to M1, the M2 is not present. Just wondering.
I appreciate your assistance.
Sorry I'm not familiar with the remote controls that you have now, I haven't seen them before, but you cannot have two working thermostats in circuit otherwise they will interfere with each other. It may be, that if you leave the existing controls in place and set them to maximum / permanently on, then the Nest will work.

Otherwise it seems from the instructions that tell you how to install it that it is an optional extra, so you maybe able to reverse the installation instructions to restore the boiler to its original condition. The drawings you posted show different options too. One has several zones. If you do have more than one zone each zone will need a separate Nest.
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Stern, with the Baxi AVS77 thermostat I have, it controls the water temp and heating, so there are dozens of settings, I believe you are correct, I need to reverse the installation, but of course, that is easier said than done.
I think I will reach out to BAXI for assistance in getting my boiler back to factory settings.I do appreciate the assistance. I will post response from Baxi, so maybe this info may be helpful to others.

found a solution to Nest Install on Baxi Luna 3 Comfort boilers with Baxi AVS77 thermostats.
1. If Baxi AVS77 thermostat is installed on the boiler, no problem, leave it there, also on my boiler the AVS77 was connected
to the M2 (optional connection) terminals 1 & 2.
2. If Baxi AVS77 is installed in the house, remotely from the boiler, you must install it on the boiler.
3. To install on boiler, the AVS77 is made to fit on the Baxi Boiler cover, use your existing wires, that run from the boiler to the thermostat in the house, and just cut the wires off, when you mount the AVS77 on the boiler.
4. This boiler was made to operate with the AVS77, so it must remain connected to the boiler, I could not figure
out how to completely remove it, but installing on the boiler cover is a simple process, and you do retain all the
AVS77 controls, settings, water temp, hot water temp, etc.
5. OK, so now you have installed the AVS77 on the boiler, in order to install a Nest Thermosta, and for it to work, you have to
change 1 setting in the AVS77. On the AVS77 thermostat, press top left button three seconds to access "IP Settings"
then press OK button until "AMBON" appears on the screen, you should see also a number "1" on the display, press the
minus button and change setting to zero "0", then press IP button again to save this setting. Doing this you are telling the
boiler that the AVS77 is installed on the boiler. Also by doing this, it enables you to install another thermostat in your
6, I installed the Nest Heat Link, 1 meter from the boiler. I connected the N & L wires to the Heat link for power, I did not
use the N & L wires on the boiler I basically connected a two wire extension cord to plug into an outlet close by.
6. I connected two wires from the BAXI boiler M1 Connector, terminals 1&2 to the Nest Heat Link terminals 2 & 3, then I
connected my old existing thermostat wires to T1 & T2 on the Heat link, and installed the new Nest Thermostat where my
old AVS77 thermostat was installed in the house, and connected existing 2 thermostat wires to thermostat base.
7. I installed the nest thermostat, and went thru the installation menu, I selected "combi boiler, during the installation.
New Nest thermostat works great as advertised, and I have the old AVS77 thermostat still on the boiler to make any changes to the boiler setting that I may need.
I hope this info helps any future Nest Installations with a BAXI boiler with AVS77 thermostat.

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