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Nest thermostat battery keeps draining
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I see that quite a few posts discuss Nest Thermostat low battery problems.  I have read them but haven't found a solution to my problem.

I have a Nest 3rd Gen.  Installed in January 2020.  Worked fine from install until this week, when I found the thermostat off, no farsight, and not heating.  (This furnace and thermostat are in my basement, and in the pacific northwest we would use a bit of heat early each morning, there given the weather even in June.)

To get the thermostat working again, I charged it up via its USB charger.  That lasted about a day, but then battery drained again.

Tried resetting network connectivity so device doesn't waste battery on wifi.  No change.

Single-stage 80% furnace, wired with common line to thermostat.  Voltage screen shows is Voc 36.34 V, Vin 36.34 V, lin 200mA (c).

Looked inside my furnace.  Don't see any fuse to replace.  Anyway, the voltage described above is in spec, so I don't know what good a fuse change could do.

Feel like this should be a simple install that works well and reliably, as it did upon install.  Would very much value any suggestions of what to do to get this resolved.

Photo of thermostat wiring below.  Yellow wire is present in the wiring bundle, but disconnected from thermostat and also from furnace, because this furnace has no AC, only single-stage heat.



And device diagnostic screens pertaining to wiring and power:


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Hi Bged,
 
Thanks for bringing this up. Nest thermostat uses the voltage from your system’s wires to keep its internal battery charged. There might be insufficient power from the wires or the system that causing the Nest Thermostat to drain faster.
 
Here's the normal power reading:
  • Power: 3.8 V and above
  • Voc: 29 to 42V
  • Vin:
    • 29 to 42V when your system is not running
    • 6 to 7V when your system is running
  • Iin: 20 to 40 mA
If there is a C or common wire in your thermostat:
  • Voc: 29 to 42V
  • Vin: 29 to 42V
  • Iin: 100 or 200 mA
 
Let's try these troubleshooting steps below:
  • We can also try to disconnect the device on your wifi network for a day and monitor it. Go to Settings>Reset>Network and reset all network settings. This will make the thermostat not attempt to connect to Wi-Fi. See if the battery draining continues without Wifi. 
  • Your system may have a blown fuse. A blown fuse on your system’s control board can prevent power from reaching your thermostat. Contact a Nest Pro in your area to check your system and your thermostat wiring.
  • Try reinstalling your old thermostat. If your system works as it should with your old thermostat, your Nest thermostat may be damaged and needs to be replaced.
Let me know how it goes.
 
Thanks,
Celyne
 
 
 
 
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Celyne, thanks for replying. Looking at your diagnoses and suggestions:

My power readings are within spec.  I am already disconnected from wifi, but battery drain continues.

My furnace can't havea blown fuse preventing power from reaching my Nest, because my Nest's power readings are normal.

I reinstalled my old thermostat.  It works perfectly.  

Sounds like your diagnosis is that my Nest thermostat is damaged and needs to be replaced.  That is my best diagnosis too. How do I proceed?
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Hi Bged,
 
Thanks for the update. Let me send a private message to further assist as we need to gather some information that cannot be posted publicly.
 
Thanks,
Celyne
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hello,

Please send me a private message as well. Inam in the same boat. It worked perfectly until this week. I did all of the same trouble shooting and have 200ma on lin as well
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Relevant Answer
Hi Adam, 
 
We're glad all are working as intended and thanks for sharing your thought here, appreciate it. I'll go ahead and lock this thread. For any questions, comments or concerns, please feel free to start a new thread and we'll be happy to help.
 
Thanks,
Celyne
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