Google nest would not communicate with furnace

[ml61]

Just had a technician here because heat not working. Problem was with the Nest. Tech showed how furnace works fine, but Nest not communicating with it. Reinstalled prior thermostat and now getting heat.

Background: installed nest last April. AC worked fine. First cold day today, realized heat not working.

[humbertogarcia]

Hi ml61,

Thanks for posting in the community and for providing detailed information about this situation! I understand that your Nest Thermostat was connected last April and didn’t heat with the first cold. I'm glad to hear you have heat again. The fact that the old thermostat works but the Nest doesn't is an important clue that points to a specific wiring issue.

To help us get to the bottom of this, please provide a few more details:

• What is your specific Nest thermostat model?
• Did the technician mention any specific details about the wiring or power they found?
• Is there an error message when rewiring the Nest Thermostat, if this was tried?
• Could you send me a picture of the wires connected to your Nest and the wires on your old thermostat?

Once I have this, I can provide the right troubleshooting steps.

Regards,

Humberto

[ml61]

The problem was that the nest could not detect the C wire -- the Nest indicated this and the technician confirmed it, and that the wire was connected properly. I bought a new Nest yesterday, and had the same exact problem. 

As for the model, the boxes these came in just call them Nest Thermostat. The SKU on one is GAO1334-US, if that helps.

[humbertogarcia]

Hi ml61,

Thanks for the prompt response and for providing all those details. I understand that sending a picture of the wiring isn't practical right now, but it's helpful to know what the technician found and that a second Nest Thermostat had the same issue.

According to your report, the problem isn't with the Nest Thermostat itself, but with how it's getting power from your furnace. Even though the technician confirmed the wiring was correct at the thermostat and your furnace works, the Nest still isn't getting the constant power it needs.

There are a few reasons this could happen. For a complete description, read the article "Learn about the common or C wire."

• The C wire isn't connected to the furnace's control board. Sometimes a wire is there, but it's not actually attached to the "C" terminal at the other end.
• The C wire is broken. If there's a break or a short in the wire inside the wall, it won't be able to deliver power.
• The furnace isn't providing enough power. Some older or less common systems don't provide a consistent 24V of power on the C wire.

The good news is that there's a simple solution for all these situations. The Nest Power Connector is designed to provide a constant power source to your thermostat without needing a working C wire. It's a small accessory that you can install at your furnace's control board, and it will fix the power issue that both thermostats are experiencing.

To get your Nest Thermostat working, I recommend installing the Nest Power Connector. It's the most reliable solution for this problem and will get your heat working quickly.

Please keep me posted with the results, I’m here to assist you.

Regards,

Humberto

[ml61]

There is ample power through the C wire. The technician connected it to the corresponding wire for the furnace, and the furnace turned on -- so no broken wire or short, and the C wire is connected at the furnace end. Our house was newly constructed last year, so a brand new furnace.

When I stripped the wire, it appeared to be a 20 gauge. Maybe that is the problem?

[humbertogarcia]

Hi ml61,

Thanks for the quick follow up and for the additional information. I appreciate you taking the time to confirm the wire gauge and for providing a detailed report from your technician.

The fact that the technician used the C-wire to successfully turn on the furnace is a key detail. This confirms that the wire is not broken and has power at both ends. It also confirms that the 20-gauge wire is suitable for providing power from your furnace to the thermostat.

Based on everything you’ve described, it sounds like the issue is a compatibility problem with how the Nest Thermostat is sensing the power from your furnace, rather than an issue with the wire itself. This is sometimes seen with certain new or less common HVAC systems.

The solution for this specific situation is the Nest Power Connector. This accessory is designed to regulate the power from the furnace and ensure the Nest Thermostat gets the consistent signal it needs, even if it has trouble detecting the C-wire on its own. It provides a reliable power source and a clear signal for the thermostat.

You can find more details on why the Nest Power Connector is the best fix for your issue in our previously mentioned help center article: Nest Power Connector.

I am confident that installing this accessory can resolve the problem and get your Nest Thermostat working with your heating system.

I suggest trying it and keeping me posted in order to confirm the outcome, I’m happy to assist you.

Regards,

Humberto

[ml61]

I'm confused. Most of what I'm seeing on the internet is that the power connector is used when there is NO c- wire. If I purchase the power connector anyway, do I still connect the thermostat to the c-wire or is the connector *instead of* the c-wire?

[ml61]

I won't send a picture of the wiring, as that would require me to take the working thermostat off and re-install the Nest. I can tell you that our wiring includes a yellow, green, red, white, and blue (this is the C or Common) wires. The technician verified that it was wired correctly -- all in the correct slots and the tabs pushed down. Outside of the Nest, he connected the red to the C wire, and the furnace started. That is why we thought it was that specific Nest that was the problem, but now a second Nest has had the same problem.