3rd gen Nest Thermostat stopped self-charging after 8 months of working fine

[Brion]

In early 2024, I tried to get help for why my 3rd Gen Nest thermostat was no longer holding its charge. I could get no good answer, so I bought a new one and it has been working great for 8 months, but now it doesn't charge unless I connect it to a USB charger. I can charge it for a few hours and it will last a day or two and then goes out. I thought perhaps it was the voltage supplied by the HVAC system, but that has not changed and I also swapped this unit with another, older unit in another section of my house and the old unit ran fine for a week, but this newer unit in the other location also did not hold a charge or self-charge. It has taken 8 months to get to where my former unit got to in 4 years. Seems like I need to get a replacement. My wife is so mad at having to lose heat during these cold winter months, she wants me to go back to a dumb thermostat. Is this just a bad thermostat? What components inside would fail in 8 months? If I upgrade to a newer generation, will they connect to the existing wall socket? Will I need to upgrade both of my thermostats or can I upgrade just the bad/newer one?

[Jeremyg]

Hi @Brion!

Thanks for reaching out to the community. I am sorry that your Nest thermostat 3rd gen is no longer holding its charge, but no need to worry; help is here. We appreciate all of your previous troubleshooting efforts. M15 errors usually occur when you interact with the Nest thermostat after you've started a new pairing session but didn't finish it. Could you please perform the following steps:

• Once you pair the thermostat, choose a mode like Eco, Heat, or Cool.
• Then go back to the Nest app, and the app will show a circle with an exclamation mark on the Nest thermostat.
• Tap the exclamation mark and continue the thermostat configuration in the app. There’s no need to choose “Reset Device” on the thermostat.

Tell me how it goes.

Best regards,
Jeremy.

[Brion]

I set that thermostat to heat and cool mode. The app shows both of my thermostats but there is no exclamation mark. Each thermostat has its own weekly schedule for temp ranges to maintain.

[Brion]

This morning, when I tried to increase the temperature setting on this thermostat, it put up a message "your thermostat will shut down to recharge its battery" so I put it on the USB charger. I have a new 4th gen ordered as we cannot continue this way. I am hoping it is OK to have a 3rd gen and a 4th gen in the same home.

[Brion]

Thew new gen 4 thermostat came today and it seemed to install fine; however, when it turns on the heater, it stops after 1 second and then shows a leaf st the bottom, then a few seconds later, it turns on the heater and stops after 1 second showing that leaf again. What is it doing? I hear the heater start up and then shut off. I don't think this is good for the heater to start 20 times a minute.

[Brion]

I had to put the old gen 3 back on. I paid my heating guy the emergency rate of $160/hr and he could not understand why the thermostat would turn on the heater for 1 sec and then turn off and cycle that way forever. Also, after doing that for a while, it then complains there is no power, with code E448. If I USB charge it for a while, it does not complain about no power but goes through the heater cyclying on/off every 3 seconds. I don't have a C wire connected to my thermostats and never have. Am I about to discover that without the C wire I have to charge them every day? I just bought the gen 4 to get away from that. How did my old gen 3 work fine for 4 years without a C wire? The new gen 3 worked fine for 8 months.I was a bit surprised the new gen 4 came with no instructions on how to install it other than (get a pro to do it - I don't know where to locate such pros and my heating guy doesn't know much about them, but did say he sees most of them having a C wire). If that is the case, I just wish someone would have told me I need a C wire.

[Jeremyg]

Hi @Brion!

Thank you for your reply. I appreciate the information provided in the previous post that is very helpful to better understand the situation. In some scenarios the Nest thermostat display needs to be charged because even if the display is attached to the base, that does not mean it is being charged. The battery of the display is different; for that reason, behind the thermostat display you will find a mini USB port to charge it. You do not need to charge it often, depending on location. 

Here's a comprehensive guide to help you decide:

1. Does a Nest Thermostat Require a Common Wire (C-Wire)?

A Nest thermostat can operate without a common wire in many cases by using power stealing. This technique draws small amounts of energy from the heating system’s existing wires. However, relying on power stealing can cause:

• Flickering screens or intermittent reboots.
• Unexpected heating or cooling cycles, as the system activates to recharge the thermostat.

Compatibility Tip:

• The Nest Learning Thermostat is better at handling two-wire setups (red and white) due to its advanced power management.
• The Nest Thermostat (non-learning version) typically requires a C-wire for reliable operation.

2. Is It Better to Add a C-Wire?

Adding a common wire ensures consistent power to your smart thermostat, improving performance and avoiding system glitches. 

3. Things to Check Before Installing

• Voltage Compatibility: Ensure your boiler operates at 24V. Most Columbia gas boilers are compatible, but it’s worth double-checking.
• Existing Wiring Setup: Confirm that your current red wire (Rh) supplies power and the white wire (W1) controls heating.

Please keep me posted.

Best regards,
Jeremy.

[Brion]

Hi Jeremy, we did verify that shorting the Rh wire to the Wi wire (using alligator clips), the heater ran as usual. I will try putting the gen 4 back in after having charged it. The gen 3 lasts between 1 and 2 days between charges (after lasting 8 months when new without any charging). It is definitely a 24V system. If I need to charge the new gen 4 before using it, that would have been good to know in the documentation supplied with the unit.

[Jeremyg]

Hi @Brion!

Thank you for your reply. It is good to know that the heater is working fine. You encountered a new inconvenience with the battery of your Nest Learning Thermostat 4th Generation. Based on the information that you gave, that is a possible Wi-Fi problem.

Could you please try the following steps: 

• To confirm that it’s a Wi-Fi issue, can you please disconnect the thermostat from the Wi-Fi network for 24 hours?
• If the battery doesn’t drain, then the issue is likely a poor Wi-Fi connection, and the battery behavior is only a symptom.

Please keep me posted.

Best regards,
Jeremy.

[Brion]

After having charged the new gen 4 learning thermostat for several days, I connected it again and it clearly states on the display that there is no power. Of course there is just the same power that was used to run the gen 3 thermostat fine for 8 months and the one before that for 4-5 years. I gather that I need a Common C wire to give the gen 4 power to run. I believe when I checked with a Volt meter that the Rh to Wi registered between 23 & 24V AC. Would it make sense to try splitting the Rh and feed it also into C? Would that give the thermostat the power it needs?

[Brion]

Possibly I could have left the gen 4 in place as it did seem to be running the heater this time, but since it was displaying "No Power", it did not seem appropriate to let it continue on, so I switched back to the gen 3, that I have to charge manually every other day. I believe I will try one more gen 3 device and see if it might work better. I plan to order one today. I may, in the end, have to pull through a new 6-wire bundle to replace the 5-wire bundle we have now for both HVAC systems in this house. Obviously, charging your thermostats every-other day does not work if you have to travel at all, so I have to change something. My second gen 3 is working fine for the other 5-wire system in this home, so I will likely just go with another gen 3 and hope it lasts more than 8 months.

[Jeremyg]

Hi @Brion!

Thank you for your reply. This situation needs further assistance; please fill out this form with all the necessary information, like the thread title or link and your username in the community. Once you've completed the form, let me know. Someone from my team will contact you shortly to help.

Best regards,
Jeremy.

[Brion]

Hi Jeremy,

I installed the new gen 3 when it arrived yesterday, but it kept shutting down while connected and I was trying to set it up. I found I needed to charge it up via USB first and then I was able to get it set up. I never had to do that with prior gen 3 devices. I am hoping once started, it will not require further USB charging going forward. It has been 24 hours and it is doing well. I will work on getting the form filled out and let you know.

[Brion]

It has been three days now without having to recharge the gen 3 learning thermostat. It is possible that the gen 4 would also have worked OK once it was charged, but I did not like seeing "No Power" on the screen all the time as it does not give me confidence that I could go on a long trip without trouble. I'm not sure what I will do with the gen 4 device at this point though.

[Brion]

Jeremy, BTW, I did fill out the form you recommended I fill out. It isn't clear what comes as a result, but perhaps I will hear back at some point.

[Brion]

So, it has been 10 days and I have not had to recharge the new gen 3 thermostat. I believe it will work fine for at least several months before it stops holding its charge. I will hold on to the gen 4 just in case.

[Jeremyg]

Hi @Brion!

Thank you for keeping me updated. I appreciate the time you took to perform the troubleshooting steps. I'm glad to hear your thermostat is working fine now. 

Feel free to keep us posted if you have more questions.

Regards,

Jeremy.