topic Re: Heating Randomly Won’t Turn off in Nest Thermostats

Heating Randomly Won’t Turn off

Pompeyjas0420 — Tue, 24 Dec 2024 13:51:02 GMT

Hi there, after reviewing many posts and trying everything I can think of and find this is my Hail Mary before reinstalling the old generic thermostat. Occasionally/randomly the heat will keep running past the desired temp. I was keeping the temp at 70 and it would run and reach this temp and then keep running altho the app and thermostat wouldn't show that it was still running. “Heat pump” would be shown on the screen but it wouldn’t be orange as though the heat is actually on. There are a few times the temps inside have reached 75-77 deg and the only way to stop the furnace/heat pump is to flip the breaker and it shuts off and then doesn’t happen for a couple of days. I’ve noticed it was happening more when the temp was set around 70-72 and happening every couple days (less often) around 68. I have turned off all schedules, auto, and learning capability’s but at a loss as it is still happening. Any thoughts, comments or suggestions are really appreciated.
- Jason

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Tue, 24 Dec 2024 17:49:58 GMT

@Patrick_Caezza

Maybe you have some thoughts?

Re: Heating Randomly Won’t Turn off

Dolo — Wed, 25 Dec 2024 07:30:05 GMT

I’m struggling with the same issue. I can turn the system off and it turns itself back on to heat to 90

Re: Heating Randomly Won’t Turn off

moralesvicente — Sat, 28 Dec 2024 02:27:31 GMT

Hello folks,

Thank you so much for posting in this community. I’m sorry to know the thermostat isn’t working as you expected regarding the heating. Don’t worry; it’s a pleasure to help.

To provide you with accurate troubleshooting steps, I would appreciate your assistance in answering the following questions:

What type of Nest thermostat do you have? For your reference, you can use this article: How to tell which Nest thermostat you have.
When did the issue start?
What other strange symptoms have you experienced since the problem started?
Are there any error messages? If so, what are they exactly?
When was the last maintenance check for your HVAC system?
Have there been any recent changes or upgrades to your HVAC system?
Do you have a common ground wire or C wire?
Have you experienced any power outages within the last few days or weeks?

If you have any more information that could be helpful, please let me know.

Best regards,

Daniel

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Mon, 30 Dec 2024 13:59:31 GMT

What type of Nest thermostat do you have? nest learning thermostat gen 3

When did the issue start? Once the heating started coming on, never had an issue with cooling

What other strange symptoms have you experienced since the problem started? Randomly when this happens sometimes it shows heat is on, sometimes says heat pump and sometimes it shows nothing is on but the heat is actually on and running but it’s like the thermostat doesn’t realize it or know.
Are there any error messages? If so, what are they exactly? No errors or anything have ever popped up.
When was the last maintenance check for your HVAC system? July 2024

Have there been any recent changes or upgrades to your HVAC system? No it was installed in 2022

Do you have a common ground wire or C wire? C wire

Have you experienced any power outages within the last few days or weeks? No I have not

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Tue, 31 Dec 2024 21:10:17 GMT

The old thermostat wiring before switching to nest learning gen 3.

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Tue, 31 Dec 2024 01:19:38 GMT

@CoolingWizard any suggestions or thoughts please l?…I’ve seen that you’re quite a helpful chap

Re: Heating Randomly Won’t Turn off

moralesvicente — Tue, 31 Dec 2024 02:30:30 GMT

Hello Pompeyjas0420,

I appreciate you keeping me in the loop. To continue providing you with further information, could you please attach a picture of the wiring configuration in the Nest Learning Thermostat 3rd Gen?

Keep me posted so I can provide you with further assistance.

Regards,

Daniel

Re: Heating Randomly Won’t Turn off

CoolingWizard — Tue, 31 Dec 2024 14:29:03 GMT

@Pompeyjas0420 ,

When you check the power using the display , what is being reported?

Choose SETTINGS->TECHNICAL INFO->Power:

BATTERY

VOC

VIN

LIN

AC Cooling Wizard

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Tue, 31 Dec 2024 21:09:31 GMT

Thank you so much for the reply, here is the information collected from the unit.

BATTERY - 3.931V

VOC - 31.76V

VIN - 31.76V

LIN - 200 ma(c)

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Fri, 03 Jan 2025 21:15:24 GMT

Hi there, thank you for the reply. Here is a photo of the nest wiring. Thank you for your assistance. @moralesvicente

Re: Heating Randomly Won’t Turn off

CoolingWizard — Wed, 01 Jan 2025 19:08:42 GMT

@Pompeyjas0420 ,

In your original post, you stated “occasionally “ this happens. Can let me know the frequency of occurrence?

Clearly you have ample power coming from the air handler and this leaves hardware or software.
Hardware can be a defective temperature thermistor or a digital relay that is failing to open.
This could be software although not very likely.
This case should be escalated. We need diagnosis of the ambient temperature sensors (thermistors) and obtaining internal log files of the software system signaling the relay to open.

AC Cooling Wizard

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Wed, 01 Jan 2025 19:54:02 GMT

Thank you for the information and following up with me. It was happening every 2-3 days When I had the thermostat set at 70 or higher, it’s only happening once or twice a week now that I have the temperature set lower between 65 and 68. I haven’t noticed anything common when The heat decides to not shut off and keep running, like sometimes it’s during the day and sometimes it’s at night. Let me know if there’s any other information I can pull from the unit to share with you. In another comment, I shared the pictures of the prior thermostat and the new wiring to the nest if that is helpful. Thanks again! Jason

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Fri, 03 Jan 2025 21:12:02 GMT

It’s happened again just today, thermostat on 68 and not showing that the system is on but it was on and blowing full heat and the internal temp was registering as 72 in the house. It’s like it fails to realize that the temp is reached and to communicate to the heater to turn off. But the crazy thing is that it happens very intermittently and not consistent. I took a picture of what the screen looked like today but I can’t add it to this reply. In order to stop the heat from blowing I had to flip the breakers to the furnace/heat pump.

Re: Heating Randomly Won’t Turn off

CoolingWizard — Fri, 03 Jan 2025 21:24:00 GMT

@Pompeyjas0420 ,

You have a heat pump and your old thermostat had the brown wire attached to EMERGENCY HEAT. You need to move the brown wire from W1 and place in the programable * terminal. Then need to configure that as Emergency Heat. I am not saying this will fix your runaway heat problem but will correct the software thinking you have might have a duel fuel system.

AC Cooling Wizard

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Fri, 03 Jan 2025 21:57:59 GMT

Thank you for that suggestion!I have completed it.

Does this look correct? I did as you instructed, and then updated the settings in the software. Anything else you can think of that I can try? I will let you know if this happens again.

Re: Heating Randomly Won’t Turn off

CoolingWizard — Sat, 04 Jan 2025 05:57:55 GMT

@Pompeyjas0420 ,

The W2 wire should be configured as Auxiliary Heat and not alternate heat. You will need to go to SETTINGS: EQUIPMENT: PRO hit Continue twice, then you will see a picture of the backplate with colored wedges. Any yellow wedge needs attention. Rotate and select W2 wedge and select. Then change the setting to Auxiliary Heat.

AC Cooling Wizard

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Tue, 07 Jan 2025 16:59:40 GMT

I have made the changes that you have suggested. It did not stop the heating situation where it doesn’t turn off as it happened again yesterday. I took some pictures of the display screens, but I’m not sure how to send them to you because it won’t let me attach them to this reply. Can I email them to you or what do you suggest? Thank you so much

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Tue, 07 Jan 2025 17:01:06 GMT

Re: Heating Randomly Won’t Turn off

Pompeyjas0420 — Tue, 07 Jan 2025 17:04:22 GMT