Honeywell Mercury 2-wire controlling Honeywell Water Zone Valve

[Mroz]

Have an old school mercury thermostat using only 2-wires controlling a zone valve (water).

There are two un-used wires in the 4-wire bundle.  Can the 24-V power the batter ybackup in the NEST?

[Markjosephp]

Hello Mroz,

I'm sorry for the delay, and thank you for taking the time to let us know about your inquiry.

In most cases, the Google Nest Thermostats can receive power from your heating and/or cooling wires. But there are situations where you might need to connect the Nest Power Connector or a common wire to consistently deliver power to your thermostat.

Please take a look at this article about how common wire works and let me know if you have more questions.

Regards,
Mark

[Jenelyn_O]

Hi there,

Chiming in — I just want to check if you managed to see the response above. Please let us know if you still have questions or concerns, as we'll be willing to assist you further. 

Thanks for your help, Mark.

Best,

Jenelyn

[Mroz]

I did get a response.  I also looked up the water valve in the basement.  My  next trip up I will make sure I can get a power source for the new unit

[Mroz]

I found that the original install used a 4-wire bundle.  There is 24V on the Honeywell water valve in the basement.

It looks like the current 2-wire has doubled up at T-stat and valve.  I think I can break out a "C" wire

[Jenelyn_O]

Hi Mroz,

That's good to know! How is it now? Were you able to have a C wire? Please let me know how it goes.

Regards,

Jenelyn

[EmersonB]

Hi everyone,

@Mroz, we wanted to follow up and see if you are still in need of any help. Please let us know if you are still having any concerns or questions from here, as we would be happy to take a closer look and assist you further.

Thanks for answering, Jenelyn and Mark.

Best,
Emerson

[Mroz]

I have not been back to my place up north to work on this

[EmersonB]

Hello Mroz,

Thanks for getting back to us. Sounds like a plan. I'll be keeping this thread open for a few more days. Don't hesitate to post your update here.

Regards,
Emerson

[EmersonB]

Hey Mroz,

How's it going with your Nest Thermostat? Were you able to perform the steps suggested? We'd be glad to hear from you — We'd like to make sure everything is working.
 
Thanks,
Emerson

[EmersonB]

Hi Mroz,

Just one final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, we would be happy to keep it open. If there's more we can do, just let us know.

Best,
Emerson