Nest 3rd generation won’t switch to heat

[Butterflycl]

Hi, I’m hoping someone can help. I have two nests, the one that runs the bigger unit will not switch back over to heat from air-conditioning. The one that runs the smaller unit won’t switch back from heat to air conditioning. All the wiring looks fine. This has happened before. this time I can’t figure out how to fix it.  thank you!

[Butterflycl]

Also, when I do a test it directs me to the nest website and “T04 forced air system problem”

[lucasdemon7]

It is like a frustrating issue! If everything looks good wiring wise, it might be worth checking the settings in the app or resetting the Nest thermostats Board Results 2025. Sometimes a software update or a reset can help them sync properly. If that doesn't work, double check the system’s power and make sure the HVAC units themselves are functioning as expected.

[Patrick_Caezza]

@Butterflycl 

You said you have two Nests. Are the units they control separate or one unit with a zone controller?

[Butterflycl]

@Patrick_Caezza We have two units 

[carl310]

Just curious, has your thermostat updated recently? I've been experiencing issues for the last 2 hours since mine updated to the 6.3-5 update.

[Butterflycl]

Yes actually, it auto updated. @Carl310

[Djm2]

I think it might be caused by the lasted nest thermostat software update. The new update bricked my thermostat  and now I am not able to use it. It’s stuck in an update loop. 

[DeboraJ]

Hi @Butterflycl,

Thanks for contacting the community. I understand you're experiencing an issue with your thermostats not switching back from heat to air conditioning. I'm here to help, so let's see what we can do.

To make sure I understand everything correctly, could you please provide me with the following information:

• You mention that this issue happened to you in the past. Could you please tell me what steps you tried to make it work?
• Could you tell me what type of HVAC system you have for both of them?
• Could you please be able to send us a photo of the wiring setup for both thermostats? 

Once I have this information, I'll be happy to help you to get your thermostats working on heat!

Best regards,

Debora