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Nest no power alarm

Community Member

When the float switch on my AC air handler actuates indicating the drain line is plugged and the catch basin under the air handler may soon overflow, the Nest thermostat shuts down the AC system. The indication on the thermostat is "loss of power". Is there any way I can get the Nest app to send me an alert on my iPhone of this issue. It would be nice to know that so I could then check out the drain line and correct the problem. Right now I have no way of knowing that my system is shut down until I actually note the temperature getting warmer and then check the thermostat to see that it has no power and then start troubleshooting the problem. An alert notification would be nice to have.


Platinum Product Expert
Platinum Product Expert

You have a slight misunderstanding about that system, The thermostat is a slave to the HVAC equipment.  In fact, the power comes from the HVAC equipment on the R wire. When the water backs up in your air handler the float switch is wires in series with the R wire coming from the transformer.  When the float switch opens the R wire is disconnected and thus interrupts the power coming to the Nest Thermostat. 

if this is happening, it means that your condensate drain line for the air handler is plugged and needs to be cleaned.

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner. If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Hi there,

Thanks for posting in the Google Nest Community forum. I hope you get the answer you're looking for. Please let us know if you still have questions or concerns, as I'll be willing to assist you from here. 

I appreciate your help, @CoolingWizard.


Community Specialist
Community Specialist

Hi bsibul,


I wanted to follow up if you still need help. Please let me know if you’re still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.




Community Specialist
Community Specialist

Hello bsibul,


I'm checking in to make sure that you've seen our response. Please let us know if you have any additional questions or concerns before we lock this thread in 24 hours.