Nest Thermostat not heating after adding C-wire

[rgarcia12]

Early this summer I had to add a C-wire to my thermostat because the battery kept dying while running AC for an extended amount of time.  Now that it is fall, I turned the heat on and it's not working. I'm not receiving any errors, it just isn't heating at all. The  heat worked fine all fall/winter last year without the C-wire attached. Any suggestions?

[Houptee]

What kind of system do you have?

Do you have only 1 R wire on the Nest?  (Rc I assume is connected and the C)

Do you also have a Rh wire for the heating system?

Trying to figure out if you have a "dual transformer system" with 2 red wires.

[rgarcia12]

I do have a dual transformer system. I use Y1, W1, RC, and C. I have extra wires but when I connected the C, I disconnected. I believe I used to use an RH as well, but when I connected the C, it gave me an error code. 

[Jeff]

Hi rgarcia12,

I just wanted to jump in real fast to see if you saw Patrick_Caezza's reply and to see if you still needed some help on this or if you were able to get it sorted out. If you are still needing some help, just let us know and we'll be happy to continue helping.

Thanks,
Jeff

[rgarcia12]

I tried to reply yesterday but it wouldn't let me. Unfortunately I don't have my old thermostat wire configuration. I did get it functioning but it's not an ideal long term solution. I had to remove Y1 and then use my Rh that I had used before I added the C wire. 

[Jeff]

Hi rgarcia12,

Thanks for the update. I'm trying to picture how things are wired now. Are you saying that the C-wire is installed with this wire swap and that everything else is the same? Everything is functioning correctly now, aside from the wires being swapped?

Thanks,
Jeff

[rgarcia12]

No, when I want to use my AC again, I'll have to remove my Rh and tape it off, and replace my Y1.  

[Patrick_Caezza]

Do you have a picture of the original thermostat's wiring that you can post here?

You only have a dual transformer system if you have separate R wires from the AC and Furnace. Only the Nest Learning Thermostat supports a dual transformer system, and you don't need any special wiring.

When you have separate AC and heating systems, the AC side is wired to the Rc, C, Y1, Y2, G,*,  and O/B terminals depending on the type of AC you have. The heating side is wired to the Rh, W1, W2, and * terminals depending on the Heating options.

You do not need an isolation relay, so don't buy one.