I have a Nest Learning Thermostat (Gen 3) that I purchased back in 2016. It was operational in my last house, and we took it with us to our new house in 2019. It has worked flawlessly that entire time, up until now.
I have always had a wall mounted digital thermometer and hygrometer mounted next to my Nest, and they have always read the same temperature (to within 1F) historically. But I noticed a few days ago that the Nest thermostat was reading 2-3F higher than the wall mounted thermostat.
So, I found 2 other digital temperature gauges that I had in the house, to see which device was faulty. All 3 thermometers read the temperature consistently within 0.5F of each other. The Nest thermostat was still reading 2+F higher than any of the 3 thermometers.
Over time, as I watched the Nest thermostat more closely, it got to a point where it was reading 5F higher than the thermometers I had. I had noticed over the past week or so, that it was taking unusually long to cool my house, and this was causing the air conditioner to run nearly continuously. It looks like the cause of this was due to the Nest thinking the house was always warmer than it was, and even as it cooled the house, the Nest thermostat would overheat further making it "think" it was warming rather than cooling.
The above photos show the three independent thermometers at 74.8F to 75.3F. Meanwhile the Nest Android app shows the Nest thermostat at 79F. I have a separate Nest Temperature Sensor (you can see in the picture), which is reading 75F, which is in line with the other 3 thermometers. (Ignore the fact that the Nest Temperature Sensor is labeled "Master Bedroom". I originally had it in the Master Bedroom but moved it downstairs for 24h to do this test.
I did some searching in the forums and found this related post:
I also opened a support case with Nest technical support (via chat). I explained the entire situation to them, and they determined that the issue was likely due to the "WiFi chip overheating", which is what the above community post talks about.
They suggested that I run the thermostat without WiFi for 24h to see if the temperature difference goes away. I was fine running this test, but before I even bothered I asked what they would do if we determined that the WiFi chip indeed was overheating. They said they would replace the device if I could show that it no longer overheated when WiFi was disabled for 24h.
Before I ran the test though, I asked them to check the warranty status of my device, because having purchased it in 2016, I figured they would just tell me it was out of warranty anyhow. The did confirm it was out of warranty, and said that at this point my only recourse was to purchase a new $249 Nest Learning Thermostat to replace the broken one.
It was also suggested on the troubleshooting session that the issue could be related to the transmit power of my WiFi network. The technical support representative insisted I check everything in this article:
Update Wi-Fi network and router settings
I have an Eero Pro 6E mesh network, and unfortunately the settings you can toggle on the Eero devices are VERY limited. I did confirm though that ipv6 was enabled, DHCP leases were longer than 2 hours, and 802.11bgn were available and supported by the Eero Pro 6E. Unfortunately, the Eero Pro 6E has no "Power Saving Mode" (nor have I ever seen this option on any WiFi access point I have ever owned).
It could be though that the transmit power of the Eero Pro 6E was simply too high, and this was causing the WiFi chip on the Nest Thermostat to overheat (who knows). So, I went out and purchased a very simple WiFi Access Point that only does 802.11bgn and 2.4ghz.
TP-Link N300 WiFi Extender(RE105)
I configured this device as an Access Point (and not as a Range Extender) and set up a new 2.4ghz 802.11bgn network. The only device in my house connected to this access point right now is my Nest Learning Thermostat (Gen 3). I also explicitly configured the N300 access point to use "Low Power" settings, seen here:
Even with all of these changes, the Nest Thermostat is consistently reading 2F above both the wall mounted digital temperature gauges as well as 2F higher than the Nest Temperature Sensor placed right next to it.
For a workaround, I have permanently configured my Nest to use ONLY the Nest Temperature Sensors and to never rely on its internal temperature sensor any longer. So right now, here is what my Nest looks like:
The "Downstairs" Nest Temperature Sensor is the one that is mounted on the wall next to the Nest Learning Thermostat (Gen 3). The "Master Bedroom" Nest Temperature Sensor is upstairs, in the master bedroom.
As you can see, the Nest thermostat itself is still reading 2F higher than the Nest Temperature Sensor placed right next to it.
Granted, I got 8 years out of this particular thermostat. But this particular failure mode is very distressing, because it could actually harm HVAC systems by causing them to run excessively long (or continuously) because the thermostat is failing to accurately read the house temperature.
I believe this issue is more than just a warranty concern, I think it actually could be a safety concern and Google/Nest should acknowledge the issue and offer replacements to anyone with this issue, before their faulty hardware causes thousands of dollars of damage to complex and expensive HVAC systems (both heat pumps and air conditioners could be impacted here, and I have both).
For the time being, I'll continue to run my existing Nest Thermostat with the 2 add on Nest Temperature Sensors as described above, until some other failure causes me to have to replace the thermostat entirely.
Regards,
Perry
Just so folks are aware of the severity of the issue with the Nest Learning Thermostat, here is an image that shows how broken it is.
The Downstairs temperature is a Google Nest Temperature Sensor (placed literally right next to the Thermostat) and is reading a whole 4 degrees F lower than the Nest thermostat itself. The 71F temperature is accurate, as I have confirmed it with other thermometers manually. But the Nest Thermostat thinks it is 4 degrees F warmer than it actually is.
A horribly broken product and if you've owned it for 2 years or more, that's your problem to fix apparently, not Google's.
In related news, I had a second Google Pixel 5a 5G brick yesterday. Happened to my wife's Pixel 5a 5G a year ago and now it looks like those phones are 2 for 2 on bricking completely and unrecoverably.
Word of warning: Don't buy hardware from Google. The quality is awful and they don't support it well.
