Installing an additional Nest but instructions new one needs external power; why? wire: R & W

[drschab]

I"m confused as to why I now need the external power, when my other Nest did not need it.

[Houptee]

If this is the Nest (Not the learning model) then it needs a C wire.

You need the C wire because it needs power all the time it gets (+) from R wire and (-) from the C wire.

W is the signal to turn on the heat.

Your old Nest probably had more than just R W wires and it sometimes can get enough power from the other wires (if it was a Nest Learning model).

Usually you can run a new cable just buy 5 conductor thermostat wire at Home Depot and tie it onto the old wire and pull it down thru the wall into the basement or up into the attic. It is normally not stapled to the studs inside the wall but it might be then you have to use other method to snake it into the wall.

[Markjosephp]

Hello folks,

I appreciate your expertise here, @Houptee.

@drschab, I hope you've got the answer you're looking for. If you're still in need of assistance, feel free to let us know.

Regards,

Mark

[EmersonB]

Hi everyone,

@drschab how's it going with your Nest Thermostat? Were you able to read the information that Houptee has shared? In case you have an update, you know where to find us.

Thanks for answering, Mark and Houptee.

Thanks,
Emerson

[Markjosephp]

Hi drschab,

I'm checking in to make sure that you've seen our response. Please let us know if you have any additional questions or concerns before we lock this thread in 24 hours.

Thanks,

Mark