Nest Thermostat in heat mode, after 10 mins it blows cold air

[TKYang79]

I live in San Diego so it doesn't get crazy cold here, but my heating unit started giving me issues about 4-5 years ago. It would give me heat, then blows cold air from time to time, not every time. I would have to turn it off, and back on to get heat.  I've have HVAC look at it, said unit is old, may need a new one.  I had a honeywell thermostat at this time, from when I bought the house in 2012.  2020, I replaced the unit with a brand new one, but it still did the same thing, some times it will give heat, then blow cold air, would have to turn off and on to get heat again.  My old unit was given to my neighbor, who says has work flawlessly, no issues.  This winter, I've only had to get up in middle of night to restart the honeywell thermostat twice because it was blowing cold air in heat mode.  Thinking it could be the thermostat, 2 days ago I replaced it with a Nest Learning Thermostat.  The first night, I had to get up at 3am and restart the unit to get heat.  I had to do it numerous times to get 2° warmer.  It would blow hot air for 10 mins then it blows cold air.  Yesterday night, I got up at 2am and did this for an hour, restart every 10 mins to get 2° warmer.  Overnight Temps were in the 40°s here.  Today I switched it back to my old honeywell as I've never had this much issues.  So question is, is Nest a faulty thermostat?  I followed the YouTube video, white wire to OB with O selected for heat pump.  What could it be, blowing cold air after 10 mins?  

[MelbaDT]

Hey TKYang79, 

Thanks for the detailed description of your concern and sorry to hear about your experience. 

A few questions — what specific Nest thermostat do you have? When you installed the Nest thermostat, have you checked our online Compatibility Checker if your system is compatible? If yes, I strongly suggest that you have your HVAC system checked by a local technician or our installation partner, OnTech as the same issue occurred on your old thermostat. 

Best, 

Melba

[mistrdj71]

Im having similar issue, but we've had nest thermostats for about 3-4 years and new a/c unit (<4 years?) since then. Buth behavior started a couple weeks ago

Blows heat just fine, but when temp is reached out blows cold air for about 5 minutes!  Also noticed, as im walking up the screen display goes to blue for cold air, but literally only for a milisecond, then to black background  with normal white numbers; again with air still blowing for almost 5 min

 checked firmware and it says its current(6.2-22)

Had a tech come out and it never did it for him of course!  but 2 days later its doing it again

no, not using any schedules

yes, its in heat mode only

[mistrdj71]

Hi TK, i think the short answer is obviously yes Nest has a bug. 

But i had very similar issue, but cold air would blow for 10 min at end of cycle(a/c tech verified units only blow for approx 2min or less, but not cd air) anyway, i finally figured out: 1 make sure eco mode is disabled

2- make sure 'away from home' mode is also off! (this is what fixed it for me!!) found this in the nest app, not the thermostat. I see you already went back to Honeywell, and i was just about to do the same dam thing, but hopefully this will help someone else reading.

Nest is not a bad product, but the fact they haven't fixed this(bcuz we can't be the first ones to encounter this!) is a little disappointing.