Nest learning thermostat wiring

[Kookie]

Hi

we ordered a nest thermostat but realized our system is missing the third wire. Instead of getting electrician involved, do you know if the Nest Learning Thermostat can be compatible with only 2 wire set up? We used to have the first generation learning thermostat and it did work. Just want to confirm that before I made a purchase to the Nest Learning Thermostat and return the regular Nest Thermostat

[zoeuvre]

Hi Kookie, 

Thanks for posting here in the Community forum and for showing interest in our Nest Thermostats. Are you located in North America or Europe? What is the make and model of your HVAC system? And could you send us a photo of your thermostat wiring configuration so I can take a closer look? You may use our Compatibility Checker to determine if a Nest thermostat is compatible with your heating and cooling system. 

Keep us posted. 

Best,

Zoe

[Kookie]

Hi Zoe

Thanks for getting back to me.  For some reason, I don't have permission to upload any photos. I only have the W and the R wire from my wall. The HVAC is old, but it worked before with the first gen Learning Nest. The model is Payne 100U-19A Series 121. 

[zoeuvre]

Hi there,

Thanks for getting back to us. You can upload the necessary photos to your Google Photos or Google Drive, copy the link, and then send it here in this thread. Make sure to allow access to anyone with the link so I can check on it. Also, W and R wires mean you only have one heating system. Therefore, a Nest Learning Thermostat 3rd generation and a Nest Thermostat E will be compatible with it. Here's a beginner's guide to the Nest Thermostat that you can take a look at for more.

Regards,

Zoe