3rd Gen Thermostat lower

[Toledorick]

Hello, I am having some recent trouble with both my 3rd Gen Thermostat. It all started with one at first. That wasn't powering on due to not getting power via the Rh wire has it has for the past 2 yrs. I only have a furnace with 2 wires, white (W) and red (Rh). This has been the wires used for the past 2 yrs to control the thermostats. I have 2 separate zone. First floor and 2nd floor and the 2nd floor was the one not powering up for over a day.

On 1/14/24, I lost power to both thermostats.

I then contacted hvac / oil furnace tech and found out that my 24v transformer had gone bad. A new was installed. I was able to see that both thermostat turned on and manually was able to turn my furnace and call form heat with both thermostat.

However, I'm still getting no power to either thermostats, it shows low battery and won't connect to the internet. But I can manually control the heat. 

What could be wrong? 

[zoeuvre]

Hi Toledorick, 

Uh-oh! If you've recently experienced a power outage and had your 24V transformer replaced, but your Nest thermostats are still not receiving power and showing low battery, there could be a few possible causes for the issue. Could you send us a photo of your previous thermostat wiring configuration and a photo of how the wires are connected in the Nest Thermostat base? Also, check on the following:

1. Verify that the wiring connections at both the thermostat and the furnace are secure and properly connected. Make sure the wires are securely attached to their respective terminals and there are no loose or damaged connections. Double-check that the white wire (W) is connected to the W terminal and the red wire (Rh) is connected to the Rh terminal.
2. Use a multimeter to test the voltage between the Rh and C (common) terminals at the furnace's control board. You should measure around 24 volts AC. If the voltage is significantly lower or non-existent, there may still be an issue with the transformer or the wiring between the transformer and the thermostat.
   1. Set the dial to 200 VAC.
      • If the multimeter doesn’t have a 200 setting, choose 100 or 250 VAC.
      • The general rule of thumb is don’t set it too high (500+) or too low (50).Place the red lead on the R wire.
   2. Place the black lead on the other wire being tested (W1, Y1 or C).
   3. The normal readout should be somewhere between 20 and 30 V (24 V is most common).
3. Some furnace control boards have a fuse that could blow during a power surge or other electrical issues. Check the control board for a fuse and inspect it to see if it's intact. If the fuse is blown, replace it with a new one of the same rating.

Keep us posted. We're happy to help.

Best,

Zoe