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Nest themostat not cycling heat

Community Member

I manage the maintenance of an apartment community that has decided to deploy Google Nest thermostats in every unit. I have two Nest Learning thermostats that are having the same issue and I can't find any documentation of how to resolve it. The issue is as follows:

When the Nest says it is turning on the heat the fan turns on in high speed and a short bit later (no more than 2 minutes) turns the fan off.  There will be a pause of less than two minutes and the fan will cycle back on; again, only running for a minute or so. I've checked the air handler and determined that the Nest is NOT energizing the "Call for heat" wire (White). It is, however, energizing the "Call for fan" wire (green). I've tried changing several of the settings and have done a complete factory reset; no change in behavior.  When I swap out the Nest for another, known good, Nest the problem doesn't occur.

The Nest is set to:

-Electric Heat

-Not in ECO mode

-Set to heat with target temperature 5-10 degrees higher than indicated ambient temperature

-Both are Nest Learning Thermostats. According to label the item # is T3008US

Any suggestions of where to go from here? Is there a way to do a firmware update on the Nest if it's connected to a PC?



Community Member

Having a similar issue. I have mine set to run the fan continuously. Yet once or twice a month the fan starts to go in and off.

A few days ago after this it went into eco mode.

Then my app starting showing something I've never seen before, just above where it shows the temperature at the thermostat and sensors it said something like "fan has 11 hours to run" or something like that. Then that went away.

Im also getting notations at both sensors that "The room has been slow to respond to hearing and cooling changes". That in fact is still showing.

I assumed maybe a software update to the soo and/or thermostat must have occured, but my app hasn't updated for about 6 weeks and the thermostat for 9 months.

So I'm wondering what's going on here...

Community Member

I should add the only settings change I made recently, like a week ago, was to the heat pump balance mode which I changed from max savings to balanced.

Community Specialist
Community Specialist

Hello folks,

I'm sorry for the delayed response and for the trouble this may have caused everyone. Let's see what's going on.

@TreviMaint, It appears that the Nest Thermostats are experiencing a power-related issue. The thermostat doesn't know anything about the state of the equipment. It knows it’s being asked to heat and can tell the ambient temperature and set temperature don’t match — but not why, so it just keeps trying to activate heating. Installing a C wire or a Nest Power Connector will help to avoid power issues.

Temperature schedules or Home/Away Assist could be causing the fan to turn on and off at random, @mikekovach. Running the fan longer will increase your system's runtime, so you may need to replace the air filter sooner, which might give you an alert. If the filter gets clogged or dirty, it can cause your system to shut down and give you power issues.

Please let us know if you more questions.

Best regards,


Community Member

Yes I've had the air filter discussion with my maintenance person and installed a device to measure a drop of air pressure by 50% and alert me to change the filter. That did solve problems I'd the heat strips overheating.

This is something different, randomly once every few weeks my fan turns off for a few minutes then turns back on. It may happen once, or two or three times in a day, then is good for another few weeks. Only has happened since I turned the heat on. I have my fan set to "always on" in the app.

Community Specialist
Community Specialist

Hello mikekovach,

I appreciate the details. A few questions: did you notice any time intervals or for how long the fan would stop before it turned back on? Were there any recent maintenance or changes made to your equipment before the issue occurred? Lastly, does your thermostat have a C wire?

I'll look forward to your response.



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