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Nest Thermostat

Community Member

I have a hot water boiler and a central air conditioning for heating a cooling in my house. I been upgrading the thermostats in my house from the basement to my second floor with nest thermostats . The first two are been use for heating only connected to a taco zone controller where I get my C wire from. 

Now I'm facing trouble wiring my last thermostat that controls heat in my top floor and my central ac for the all house. I been suggest by the home app based on the wires I have to use nest learning 3rd gen. but when I install the thermostat in the base does not recognized  C wire. I checked for 24 v and C wire is fine.

I been looking everywhere for information about this situation and  did not get anywhere. Does anyone had this problem solved?


Community Specialist
Community Specialist

Hello HectorAOlivera,

I appreciate you seeking answers here in the Google Nest Community Forum for your Nest thermostat's wiring configuration. I understand that setting up can be confusing when having multiple zones and thermostats. But I'd be happy to shed some light on the situation here.

A few questions: which Nest Thermostat model are you trying to install? From what country are you posting? Can you post a picture of your old thermostat's wiring? What's the message code it shows after the installation? Also, gather the power readings in the Technical Info settings.

I'll look forward to your response.


Hi Mark,

I really appreciate your  replying to me. I checked on google home app based on the wires I have witch one was gonna be the best thermostat for the application and the app recommend/suggest nest learning thermostat, that is the thermostat I'm trying to install for my third zone witch is intended to control my hot water heating zone in the winter and a completely separate a/c unit in the summer. I live in northern New Jersey, USA. I had a Honeywell T4 Pro that had no problem running the heat in the winter and ac in the summer just by switching the mode in the thermostat from heat to cool. The message nest shows is no C wire but I tested the c and rh coming from my heating zone controller and shows exactly 24 v so there is c wire and is working fine. I would l like to keep nest because I have another 2 nest thermostat for heat in the rest of the house but as right now the Honeywell looks like the best option.

Thank you

Hey there,


I'm sorry for the late reply. Thanks for providing me with more details and for keeping up with our Nest Thermostat. The common wire might not be properly grounded, so the system uses power from other available wires but doesn’t get enough energy.

To make sure, a picture of your existing thermostat's wiring diagram would help us determine how it should be labeled. Also, have you tried installing your Nest Thermostat without a C wire? Were there any changes or any power issues that appeared?

Keep me posted.