Navien NHB Condensing Boiler and Nest Thermostat

[James Cao]

Hi All - new to the forum and would appreciate some expert guidance

I would like to install a Nest to control the boiler. the old thermostat used 2 wire (R & W), which are connected to CN10 on the NHB board. I have added a blue and green wire to provide power to the thermostat but don't know where on the NHB board these wires should go.

below are pictures and would appreciate the advice.

 

[Breplum]

AC 24V will be the two terminals CN25, in your photo, hidden by the wire bundle.

 

[Sponsor]

 

[James Cao]

AC 24V will be the two terminals CN25, in your photo, hidden by the wire bundle.

Thank you! I believe the left CN25 terminal is common so blue wire here and then the C terminal on the Nest.
the right CN25 terminal is hot or grounding? so a green wire would go here? but the G terminal on the Nest is for fans? where should this wire go?

 

[Fitter30]

Thank you! I believe the left CN25 terminal is common so blue wire here and then the C terminal on the Nest.
the right CN25 terminal is hot or grounding? so a green wire would go here? but the G terminal on the Nest is for fans? where should this wire go?

It doesn't just disconnect it. What model of nest?