Installing C Wire for Nest Thermostat

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  #1  
Old 12-18-20, 10:44 PM
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Installing C Wire for Nest Thermostat

Hello everyone,

I've recently purchased 2 Nest Thermostat for my new place which has a thermostat downstairs and one upstairs. Doing my research it seems I'm going to need a C wire for them to function correctly the current thermostats are only 2 wire.

Looking at my setup I have a transformer, Honeywell relay, 2 Honeywell zone valves and a Navien NCB-240E combo-boiler as seen below.



I managed to review the wiring and excuse my diagram below but it was my best effort with microsoft paint.



Note: On thermostat #2 the black and white wire are twisted onto each other as one.
WC = Wire Cap (just the wires twisted onto each other with a orange wire cap on as seen in the photo)

After the couple of days of research online I believe in order to add a C wire for the nest thermostat i would just need to run the unused green wire on thermostat #1 and thermostat #2 to the W cable off the transformer which goes to WC5. Is this correct or am I far off?

If i was unclear i apologize in advance and will do my best to further explain if needed.

Thank you for helping!
 
  #2  
Old 12-18-20, 11:26 PM
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Welcome to the forums.

Nice diagram. I snagged it and added to it. I removed the red wires from the zone valves as they are a separate loop that the thermostats don't connect to. You are correct.... WC-5 is C.

 
  #3  
Old 12-19-20, 04:22 AM
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Hi PJMax,

Thanks for the quick response. I appreciate it!
 
 

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