Thermostat Wiring - Only R & G

[RickBerk]

I've been struggling to get my Nest 3rd Gen Learning Thermostat to work with my heating system. My system is heat only. I had an electrician try to install it, but when it wouldn't work, he gave up. 

I have two wires at the thermostat- a red and a green. There is also a white wire, that is not connected anywhere. It is not connected to the boiler, just hanging there, and is only wrapped around a screw behind the thermostat. I have no C wire. After several hours of trying to troubleshoot, I finally came to the conclusion I need a Nest Power Connector. Before I go out and buy yet another piece to this puzzle, I wanted to ask here. Is this what I need? Based on the diagrams I've seen from the manual, the only wire I can see that I would connect to the power connector would be the red. Is that right?  

Also- the electrician had the Green wire connected to the W connector. Is that right? Should it be G? Any help is greatly appreciated. It's two wires... doesn't feel like it should be this hard!

[RickBerk]

Hi Manuel, connecting the R wire to the RC terminal and G to the W terminal didn't work.

My system, as confirmed by an electrician, is a 24v system. The furnace is a newish Bosch furnace. Not sure exactly how old but my best guess is no older than 10 years based on its features, look, and condition. 

[maedacortez]

Hi RickBerk,

Thanks for your reply. When you connected your Nest Learning Thermostat 3rd Generation, did it show any lights or error messages on the display?

I look forward to your response.

Regards, 

Manuel

[RickBerk]

I got an e79.

[maedacortez]

Hi RickBerk,

Thanks for your reply. Before proceeding, I need to check if your HVAC system is compatible. Please answer the following questions:

• What is the make and model of your HVAC system?
• Could you please send me a picture of your wires?

I look forward to your response.

Regards, 

Manuel

[maedacortez]

Hi Rickberk,

Thanks for reaching out. I understand that you need help connecting your Nest Learning Thermostat 3rd Generation to your heating system. I know this can be frustrating, but I'm here to help!

As you mentioned, you only have two wires, R and G. Try connecting the R wire to the RC or RH terminal and the G wire to the W terminal.

Important: Make sure you don't have a millivolt heating system. These systems are common in older homes and aren't compatible with Nest.

Do you have an older gas furnace built into the wall or floor?

I look forward to your response.

Regards, 

Manuel