topic Re: System Blows Cold Air After Reaching Target Temperature in Nest Thermostats

System Blows Cold Air After Reaching Target Temperature

neednest56 — Thu, 20 Feb 2025 02:13:02 GMT

I am having an issue where whenever our system is heating and reach the desired temperature, the furnace turns off but the system continues to blow air that is now very cold. I have a two stage heating system, without a heat pump. I ran the troubleshooting test for both heating stages and they each took around 5 minutes for the air to turn from cold to warm, but they both ended up blowing warm air. If the air would just stop blowing from the vents when the furnace turns off, everything would be great.

Any help is greatly appreciated.

Re: System Blows Cold Air After Reaching Target Temperature

Patrick_Caezza — Fri, 21 Feb 2025 04:35:37 GMT

@neednest56

Is this a newly installed Nest thermostat or one that has been working and is now having this issue?

How is the Nest wired, can you post a picture of the baseplate wiring?

If you have it can you post a picture of the original thermostat's wiring?

Re: System Blows Cold Air After Reaching Target Temperature

neednest56 — Fri, 21 Feb 2025 04:51:19 GMT

@Patrick_Caezza It was installed last summer. It worked fine with cooling during the summer, but has been having this issue in the winter with the heating. Below are pictures of the nest wiring and the previous thermostat wiring.

Nest Wiring

Previous Thermostat

Re: System Blows Cold Air After Reaching Target Temperature

cardyblinder34 — Fri, 21 Feb 2025 16:15:39 GMT

It is like your blower motor might be running longer than necessary due to a fan setting. Check if your thermostat is set to "Auto" instead of "On"—if it's on "On," the fan will keep running even when the furnace shuts off, pushing unheated air through the vents CarX street mod. Some systems also have a built-in delay where the fan runs a bit longer to clear residual heat, but if it’s blowing cold for too long, there could be an issue with the control board or limit switch.

Re: System Blows Cold Air After Reaching Target Temperature

Patrick_Caezza — Sat, 22 Feb 2025 05:13:38 GMT

@neednest56

Thanks for the pictures.

Is there a second set of labels on the original thermostat under the terminal block?

Can you look in the furnace/air handler and verify the thermostat cable connections there? Just want to verify that the thermostat labels are correct.

Re: System Blows Cold Air After Reaching Target Temperature

DeboraJ — Tue, 25 Feb 2025 04:26:42 GMT

Hi @neednest56

Thanks for reaching out to the Community! I understand that you were having some issues with your Thermostat Device and your heating system. I know how frustrating this issue can be, so don't worry! Let me help you with that.

Before we continue, I need some information to provide you with more accurate steps:

Does the thermostat screen indicate that it’s actively calling for heat?
What type of furnace do you have? (gas, electric, etc.)
When did the heating last work?
Did the heating ever work with the Nest thermostat?
If not: Did the heating work with the previous thermostat?
Did you turn off the HVAC system?
Did you recently turn off any breakers?
Have you recently experienced a brownout or blackout?
Is there a light switch near the heater that controls an outlet?
Did you select the correct fuel type on the thermostat?
When was the last time you changed the furnace's air filter?

Once you have this information, I will be more than ready to assist you!

Best Regards,

Debora