Nest Thermostat turns fancoil system off, then back on 1 second later every few hours

[IanLangdon]

Hi all I have not been to find the answer to this in support.  My nest thermostat is hooked up and working perfectly.  However every few hours The nest turns off the fan coil unit, The nest stays powered, it's in the family will turn on about 1 to 2 seconds later.  

II've done a factory reset and disabled all Eco modes.  I should note here I do not have a c wire and the system function is fine without it.  Well except for this little issue.  😉

This is hooked up to a condominium fan coil unit, 

[Markjosephp]

Hello IanLangdon,

Thank you for taking the time to let us know about your inquiry. Let's sort this out.

To isolate:

• Gather your thermostat's power readouts: Check Settings > Technical Info > Power.
  • A power reading below 28.28 volts on the thermostat display may indicate a power problem if the HVAC system is behaving in unexpected ways.
• Does your previous thermostat have a common wire installed?
• When was the last time you changed your air filter?
  • If the air filter is dirty and needs to be changed, I'd suggest replacing it.
• Restart your thermostat to refresh it and monitor it for 24 hours.

Keep me posted on how it goes.

Regards,
Mark

[IanLangdon]

Thanks for this the power readout is battery 3.830 volts, VOC 35.15 volts, Vin 8.17 volts, Lin 20 milliamps.

Filters clean never had this problem before I changed it over from the old Mercury by plate thermostat from the '80s. ;).

There is no common wire but from what I understand, a battery bvoltage above 3.6 volts means, common wire is not necessarily needed. But perhaps I'm wrong. I have restarted the thermostat but I will restart again just to be sure.

Thank you very much for your reply I appreciate it.

[Markjosephp]

Hey there,

I'm sorry for the late reply, and thanks for the additional details. If the battery level is over 3.6 volts, then the battery is in excellent condition. However, if the line level is under 20 mA, you’ll experience low power issues. For long-term use, use a 24 V common-wire transformer. When the HVAC system is not offering enough power to your thermostat, you'll need this to provide additional power to it.

Please take a look at this article and let us know if you have more questions.

Regards,
Mark

[Markjosephp]

Hi IanLangdon,

Checking back in — how's it going? Still need our help?

Thanks,

Mark

[Markjosephp]

Hello there, IanLangdon,

It has been a few days since your last reply, and we're going to lock the thread within 24 hours. If you have any questions, please feel free to create a new post.

Best regards,

Mark

[IanLangdon]

If the solution is. Common power, then if I removed the nest  and fully charged via usb, it should not do this behaviour right?   I m nothing times when it happens.  I've noticed doing it at about 4:30 p.m. on a couple of occasions.  So if I was to fully charge the unit via USB while it was disconnected and say put it back on it 4:00.  If it then happens at 4:30 still with this negate it being a power issue or could it still be a common wire issue.  I just don't want to put the expense in if it's not a common wire issue.  If this behavior is for sure common wire I'll get one.

Thanks!

Ian.

[Markjosephp]

Hello Ian,

Thanks for getting back to us with additional details. With that said, we can verify its battery behavior by disconnecting it from the Wi-Fi network for 24 hours. Let's give it a try and observe its behavior to see if it's still draining its battery. Then, monitor its power info in the Technical Info settings.

Please keep me posted.

Regards,
Mark

[Jenelyn_O]

Hi there,

Chiming in —  I just want to check if you managed to see the response above. Were you able to try the troubleshooting steps that has been provided? Please let us know how it goes.

I appreciate the help, Mark.

Best,

Jenelyn