After 3 years, Nest now heating in cooling mode

[Dave_in_PA]

I've read others with this issue but have found no fix.

My heat pump is 3 years old. I had my HVAC contractor install the Nest learning thermostat at the same time. It has worked flawlessly until about 1 month ago.

I sleep in a cool house and when we had a few abnormally warm days this winter the house got very warm. Therefore, I sometimes turn on the AC for an hour or 2 to cool down the house before bed, 

I have noticed that when the Nest is set to cool, the heat comes on. I had my HVAC crew out and they checked the equipment and confirmed it is a thermostat issue.

I changed the O/B wire setting and nothing changed. I reset the thermostat and nothing changed. After resetting the thermostat I changed the O/B setting and still getting heat.

Any solution would be greatly appreciated as my HVAC company knows very little about the Nest and want to install a Honeywell smart thermostat. 

https://imgur.com/a/08iXaMp 

https://imgur.com/a/RAdnCmE

[CrxHybrid]

I’ve had the same issue with three of these thermostats. It has been an internal failure each time. They fail to energize the reversing valve and you get heat instead of cooling. You may attempt to get it replaced by Google but your best bet is to go with the Honeywell or a different manufacturer.  This is an ongoing issue that Nest and Google haven’t addressed. 

[Dave_in_PA]

Honeywell it is.

[Popup4t4]

Just got the ecobee since i am conveniently out of warranty for this 250 dollar thermostat lol

[Dave_in_PA]

I regret not listening to my HVAC company and installing a Honeywell from the start. I have friends that have the Ecobee and like it. 

[zoeuvre]

Hi folks,

Thanks for chiming in, @Dave_in_PA. 

@Popup4t4 and @CrxHybrid, yikes! I'm sorry to hear that you're experiencing heating in cooling mode with your Nest Learning Thermostat. It can be frustrating when the thermostat is not functioning as expected. A few questions: 

1. Are you located in North America or Europe? 
2. Is the Nest Thermostat newly installed?
3. Did you use the Compatibility Checker tool to confirm the thermostat's compatibility. 
4. Does the thermostat screen indicate that it’s actively calling for heating? 
5. What type of furnace do you have? (gas, electric, etc.)
6. When did heating last work? 
7. Did heating ever work with the Nest thermostat? 
8. Did the heating work with the previous thermostat? 
9. Did you turn off the power to the HVAC system? 
10. Did you recently turn off any breakers?
11. Have you recently experienced a brownout or blackout? 
12. Is there a light switch near the heater that controls an outlet? 
13. Did you select the correct fuel type? 
14. Do the LED lights blink on the HVAC control board? If yes, locate the light. 
15. When was the last time you changed the furnace's air filter? 
16. Have you experienced extremely cold weather lately?
17. Is this the first notable temperature drop of the year in the area?

I'll look forward to your responses. 

Best,

Zoe

[Popup4t4]

I came to this forum because my Nest Learning Thermostat recently just started exhibiting the behavior of heating while in the cooling mode and I was going crazy trying to figure out what I could have done wrong. It worked a few months ago in August/ September but now I just started trying to cool again and it heated my apartment by 10 degrees. What is the process for getting a replacement? Is there a workaround?