How to tell what disconnected white wire is doing

[Reverence]

Hi. So I have 2 thermostats that run hydroponic baseboard heat using an oil fired boiler in my house (no central air conditioning). Looking to replace the thermostats with Nest Thermostat 2020 version which I believe only work with a common wire.

However, I don't think I have a common wire (but maybe I do?).

Both thermostats have 3 wires, a white, red, and green.

The red is connected to power, the green is connected to heat, and white is just not connected and unused.

I know typically white is used for heat, and green for fan, but it seems like the green wire is being used for heat. So, I don't know if I can use the white as common or figure out what it's doing?

I tried checking the wiring on my boiler (admittedly there are a lot of wire boxes, so not sure I'm looking in the right place), but seems like it has the red connected to power and white connected to heat (which doesn't seem to make sense unless I'm looking in the wrong place because the boiler box I'm looking at seems to be connected to my hot water heater and not my boiler heat zones, or when they wired the thermostats they swapped the white and green wires).

Any idea how to figure out what the white does? If I can get this setup working with the Nest Thermostat? Or if I would have to try the C Adapter or nest learning thermostat which supposedly supports 2 wire connections.

Pictures attached. Thanks.

https://drive.google.com/drive/folders/19SoUeEcChsuQGUrVyMxQdfk1XWX00Igt 

[Ryan_G]

Hey Reverence,

Thanks for reaching out here in the community.

I really appreciate you including all the photos in your post. As I looked at them, the white and red wires are being used as power and the green wire is for heating (W). This is compatible with the Nest thermostat but we need to verify the wire configuration as the terminal and wire color is not what it looks like connected to the main board. The technician who installed your old thermostat must've put in a relay to get to the 3 wire setup to your current thermostat.

Also, it would be difficult for us to check how the wire runs from the main board to the terminal but you can try to connect these 3 wires to a Nest thermostat and we'll check if there will be any error message once it's done.

Regards,

Ryan

[Reverence]

Hi Ryan.  Thanks for the info. Are you saying this will work with the regular nest thermostat (non-learning), or only the learning one?

When I ran through the compatability wizard it said I would need a common c wire adapter to get it to work. If you're saying you don't think that would be needed, I'll give it a try connecting the wires without the common and see how it goes. How'd you recommend I connect them? Red to power, green to heat and still leave the white disconnected?

[Ryan_G]

Hey Reverence,

Thanks for the reply.

Your system is compatible with all the Nest thermostat models. It is up to you which Nest thermostat you're going to use as it will only be the same connection to its terminals.

Also, we are going to follow the same wire connection from your old thermostat.

Let us know how it goes by replying to this thread.

Best regards,

Ryan

[Ryan_G]

Hey Reverence,

I just wanted to follow up and see if you're still in need of help. Please let us know as we would be happy to answer any questions you may have. 

Best regards,

Ryan

[Reverence]

Haven't tried it yet; will try it this weekend and let you know.

Is there a possibility that using the same wire connection setup the Nest won't have enough power to run it and it could cause problems with battery drain on the nest, wifi not staying connected, or kicking on my system when it's not suppose to?

[MelbaDT]

Hey Reverence, 

I understand that it's been a while but I wanted to ensure that everything is good here. How's your thermostat now? Still need our help?

Best, 

Melba

[MelbaDT]

Hi, 

We haven't heard from you in a while so we'll be locking this thread if there is no update within the day. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the Community.

Best, 

Melba