10-02-2022 04:35 AM - edited 10-02-2022 04:43 AM
I have an older boiler that uses Taco Zone valves. I am trying to add a Nest 2020 thermostat and I do not have C wire. I bought an adapter to add 24 V for the power. The wire exiting the the old thermostat goes to the zone valve and completes the loop to energize the valve to open when there is a call for heat. The Taco valve works off it’s on 24 V transformer. If I add a thermostat add on 24 V C wire ( one wire to the C and one to the R) I would think the zone valve would stay open. Can power be added to this and how?
10-02-2022 06:16 AM
Does your Nest have both Rh and Rc terminals or only R?
If you have Rh you put Red there and White to W1 and then the AC transformer wires go to C and Rc
If you only have R on the Nest then you combine your Red wire with one wire from the Ac adapter and other wire goes to C
Here is a video that should help
https://www.youtube.com/watch?v=yi5kfn3bmEk&ab_channel=OneHourSmartHome
10-03-2022 09:36 PM
The thermostat terminals on a Taco Valve Controller typically are looking for a switch closure (like a light switch).
You'll need an external 24Vac transformer and the Google Nest Power Connector.
This is an example of how it could be wired.
10-06-2022 02:16 PM
10-10-2022 11:31 AM
Hey Cks,
I just wanted to follow up once more to see if you were still needing some help here. If so, just let us know.
Thanks,
Jeff
10-11-2022 12:26 PM
Hi everyone,
Just one quick 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, I would be happy to keep it open. If there's more we can do, just let me know.
Thanks,
Jeff