Navien NHB Condensing Boiler and Nest Thermostat

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James Cao

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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.

PXL_20210930_200040197.jpg
PXL_20210930_200052220.jpg
PXL_20210930_200056514.jpg
 

James Cao

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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

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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?
 
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