Nest thermostat randomly changes temperature setting to 19 degrees C

[JBurr]

This problem started on August 14, 2023

• August 14th between 9:30 and 10:30 at random times Nest Thermostat started setting itself to 19° C.
  • In the history log it shows the 19° setting as being “Set by the Web or Nest app.”
  • Checked all settings in the nest app and Nest on my PC.
• August 18th I removed all entries from my Nest schedule
• August 19 ~2130 thermostat again set itself to 19° C

After doing some investigation I found the following on the thread:

•  Nest randomly changes temp to 50 or 90 degrees

RyGuy71

  Community Member

In response to Divamac

‎08-14-2022 10:17 AM

I am surprised this is happening to a newer Nest thermostat. I have one that is now 7 years old and just this summer it started randomly turning cooling down to 19 C (66.2F). The AC could run for hours before anyone notices if we are even home. It is not scheduled to do this nor has anyone touched the manual or app controls. It just wastes energy and causes my Hydro bill to increase needlessly. 
Nothing has been changed since it was physically set up 7 years ago.
The only thing that has changed are periodic software updates directly from Google to the thermostat. 
I would certainly like to see any logs detailing what action was taken when the thermostat was turned down. 
This just happened a few minutes ago that I noticed the AC running, checking it to find cooling set at 19c and put it on eco for now. Normally we have it set around 23 C (73.4 F) during the summer. 
Nowhere in the schedule does it have 19 C set, but I have just turned the learning option off now so we’ll see if this helps at all. 
I would say this just started happening for me within the last month. 

It appears to me that some type of Software or Firmware update has been applied to Nest Thermostats that is causing this bug.

Model	Display-3.4
Backplate model	Backplate-5.3
Serial no.	################
Software	6.2-27
Updated	May 3, 2022 11:13 PM

Anyone else have this problem?

[JBurr]

This is the log entry that gets made in the Energy  History log when the set temperature inexplicably gets changed due to what appears to be a Nest thermostat (software) fault.

This fault appears to affect both Heating and Cooling Cycles, and this has been identified by myself and other Nest Thermostat users.

If this fault were to cause overheating of the HVAC system which in turn caused a fire and a house burned down, then I expect the legal liability for this would fall upon Google Nest and Alphabet. If the insurance company were to look for someone to sue for the damages I expect that it would be Alphabet and I am quite sure that a competent Software Engineer could determine the cause from the underlying software logs from the Nest thermostat. 

This is more than an inconvenience,  it is an identified safety hazard that would appear to be the responsibility of Alphabet,  Google Nest. 

[JBurr · Accepted solution]

On August 21, 2023 I removed all connections to Google Home that were in "Works with Nest" in the Nest settings and set the Nest thermostat  to 24° C.

• The Nest thermostat has not set itself  to 19° C since this was done.

[Jenelyn_O]

Hi JBurr,

Thanks for posting in the Google Nest Community forum. I'm sorry for the delay. For the safety of our Community members, your first comment on this post was edited to remove personally identifiable information.

We appreciate you being a step ahead of us, and we are glad that the issue seems now resolved. Please feel free to let us know if you still have questions or concerns, as we'll be willing to help. 

Cheers,

Jenelyn

[Bedryden]

Can you share how to remove those other connections?

[Jenelyn_O]

Hi Bedryden,

Could you please tell us more about your request? Also, what do you mean about other connections? I'd like to help.

Kind regards,

Jenelyn