Navien NCB-240E C Wire

[XSparkleZ]

New to the board and I didn't see any posts on this yet, so I made an account.

I have a Nest Learning Thermostat Gen 3 and wish to install it on my Navien NCB-240E.
Currently, the Navien is connected to a Honeywell Thermostat with two wires: R and H; Black and Red.
The wire has a total of 3 wires; 2 are in use as per above and the third is a green wire which is not connected or used on either side.

The R and H is connected to the TT on the Navien.
Wiring diagram below:

I see a 24 VAC beside it, but I read that I would need two wires to complete the circuit and I can't just connect the unused Green wire to it and then straight to the C on the Nest. Apparently, I need another wire that connected to the 24 VAC and then to the Nest Rc.

Wondering if the above is true?

I had another thought of purchasing the Nest Power Adaptor.
It seems to provide a single C wire from the dongle to the unit.
would I be able to use this instead and connect the C wire to the 24 VAC on the Navien?

The other thought was to connect the C wire from the above power Adaptor to the Navien 24 vac on the left and connect my unused Green wire to the right 24 vac to complete the circuit.

Thoughts?

Notes:
My Navien only provides energy to my In-Floor Heat, so the Thermostat will only control it through the R and H.

Thanks in advance.

 

[Reach4]

I don't know your device.

I have a Nest Learning Thermostat Gen 3 and wish to install it on my Navien NCB-240E.
Currently, the Navien is connected to a Honeywell Thermostat with two wires: R and H; Black and Red.
The wire has a total of 3 wires; 2 are in use as per above and the third is a green wire which is not connected or used on either side.

The R and H is connected to the TT on the Navien.
Wiring diagram below:

I don't see R or N on the wiring diagram, but somehow you found them.

But whichever is R, see if one of the outside terminals of CN-25 has 24 volts AC between R and that terminal. If you have that, I think that would be your C. If you have that, and my suspicion is correct, the other would be the same as R. I am not a pro.

 

[Sponsor]

 

[Fitter30]

Cn 25 two outer terminals
Cn 10 no wires connected
Cn 10 left terminal to Cn 25. With volt meter cn10 left terminal to both cn25 one with 24v should be common one with 0 volts is the hot 24v.

 

[XSparkleZ]

I read the left of the CN25 is common and the right CN25 is hot. It was indicated that it was used for the out of water sensor.

In principle, would that mean I could just connect the Google power Adaptor C wire to the left CN25 and it should work?

Out of curiosity, is there any risk of damage to either unit if the C wire is not correctly connected?

 

[Fitter30]

I read the left of the CN25 is common and the right CN25 is hot. It was indicated that it was used for the out of water sensor.

In principle, would that mean I could just connect the Google power Adaptor C wire to the left CN25 and it should work?

Out of curiosity, is there any risk of damage to either unit if the C wire is not correctly connected?

You would think terminals would be labeled either on the strip or on the diagram. I'd check it with a meter to be sure.

 

[Reach4]

Out of curiosity, is there any risk of damage to either unit if the C wire is not correctly connected?

I don't think so, but maybe there is something I am not thinking of.

 

[XSparkleZ]

As an update, I installed the Nest Power Connector and a 24VAC Transformer.

I found this alternative on the web and followed it.
Everything seems to be working great.

Thank you all for your help.