Nest thermostat off but furnace fan won't stop running

[Bondabio]

I am having the same issue. The furnace thermostat has been turned off during the summer and is still off, but the fan spontaneously started running intermittently yesterday morning and continued to run on and off.  I tried unplugging the furnace for about 10 minutes and then plugging it back in to see if I could reset it, but it kept on cycling even though the Nest thermostat was still turned off. I then unplugged the furnace for 24 hours, removed the thermostat, plus uninstalled and reinstalled the Nest app. When I plugged the furnace back in after 24 hours it now runs non-stop.

[RenzJ]

Hi Bondabio,

Thanks for posting here in the Google Nest Community forum. We're sorry for any trouble this may have caused you. Let's see what's going on. Please answer the following:

1. Are you from North America or Europe?
2. What type of Nest Thermostat do you have?
3. Send us the current wiring of your Nest Thermostat.
4. Send us a photo of the control board wiring.

I look forward to your response.

Cheers,

Renz

[Bondabio]

Hi,

Thanks for your reply. I am in North America.

It is a Nest Learning Thermostat Display (3rd Generation). Here is a google doc that shows the wiring.

https://docs.google.com/document/d/1QhYhLq3SLwgDqX8MRKVmf5-u6VVEOifUVHM92Fpd_E0/edit?usp=sharing

Here is a link to the photo of my wiring:  https://photos.app.goo.gl/dneG3n1FFEEPfYwW8

Please let me know if you need any other information,

Thanks!

[zoeuvre]

Hello there,

Thanks for your help, Renz. 

@Bondabio, chiming in — thanks for the follow-up information. Have you also tried to remove the thermostat display for like 5 minutes and checked if the fan still runs or not? 

Keep us posted. 

Best regards,

Zoe 

[Bondabio]

Yes, I did remove the display for more than 5 minutes and the fan continued to run.😔

[zoeuvre]

Hey Bondabio, 

Got it. Please follow these steps: 

1. Shut down the HVAC system at the breaker box. Ensure as closely as possible that all power to the system is off before proceeding.
2. Safely remove the G wire.
3. Leave the thermostat display off the base.
4. Turn the power back on.
5. Wait for a maximum of five minutes to see if the suspected component still turns on and stays on with the display removed.

Let us know how it goes. 

Thanks,

Zoe 

[Bondabio]

Hi,

We turned off the breaker and removed the G wire. When we turned the breaker back on, the fan started up immediately. 

We then turned off the breaker again and removed all of the wires from the Nest thermostat. When we turned the breaker back on, the fan started up again, so I don't think that the issue is with the thermostat, but the furnace itself.  Thanks for your help, it is probably time to call the HVAC man unless you have any further suggestions.

[zoeuvre]

Hey there, 

Thanks for trying the steps I instructed, and I'm glad that we've found out that this is not caused by the Nest Thermostat. If you wish to contact an HVAC Pro technician, get installation help or HVAC service from a professional by clicking this link. 

Reach out if you have any questions in the future.

All the best,

Zoe