Nest learning 3rd gen not turning off furnace

[PatrickJ2020]

Hello, having the problem that the furnace is not shutting off when setpoint is reach on Nest 3rd gen learning thermostat.  Reading online, someone suggested bumping the nest up to above the inside temperature and then back down.  I believe this worked.  Is this a nest issue or a furnace issue?  I have dual fuel heat, primary is electric heat pump and back up is propane furnace.  We had this issue before but it went away.  Now its every day or every other day.  No error codes. I have not tried disconnecting from the wall plate but I will next time this happens.  Does not appear to have any loose wires and all the tabs are pressed.  I do maintenance on the system every spring and fall.  I can send picture of wiring. Thank you!

[GabrielaG]

Hi PatrickJ2020,

Thanks for reaching out to the community. I am sorry to hear that your Nest Learning Thermostat 3rd Gen is not turning off the furnace, but there's no need to worry: I'm happy to assist you right now.

To get a better understanding of the situation, please help me out by answering the following questions:

• When did the issue start?
• What other strange symptoms have you experienced since the problem started?
• Does the thermostat screen indicate it’s actively calling for heating or cooling?
• Can you please send me a picture of the Nest Learning Thermostat 3rd gen wiring?

Any additional details you can provide will be helpful.

Regards,

Gabriela

[PatrickJ2020]

Thank you. It started being constant two weeks ago but it has happened before in the last year ever since I got this new nest.  No other symptoms.  When the problem is occurring, it does not indicate that it is calling for heat.   It does indicate calling for heat when working properly. I don’t see an option to attach a photo.

[PatrickJ2020]

 

[GabrielaG]

Hi PatrickJ2020,

Thank you for your reply. I appreciate the picture and the information you provided me about your Nest Thermostat. I’m happy to continue assisting you right now.

Let's try some troubleshooting steps. I recommend changing the Heat pump orientation in your Nest Thermostat. Please follow the steps below:

1. On your thermostat, go to Settings.
2. Select Equipment.
3. Select Continue.
4. Select Heat Pump.
5. The Nest Thermostat defaults to an O setting for heat pumps. 
• If the O option is highlighted, select B.
• If the B option is highlighted, choose O.
6. To make sure the issue is resolved, test your heating and cooling again.

Let me know how it goes.

Regards,

Gabriela

[PatrickJ2020]

Ok I have done this and it does turn the heat on.  I won’t know if the issue is resolved unless the issue happens again.  What does the changing setting do? How can I tell which wire is correct?  Thank you for your help 

[GabrielaG]

Hi PatrickJ2020,

Thank you for keeping me updated. I appreciate the time you took to perform the troubleshooting steps with me. I'm glad to hear your thermostat is heating now. I understand you want to know what changing orientation does and how you can know which wire is correct. I'm happy to respond to your questions right now.

If the system starts to blow cool air when the Nest thermostat is in heat mode (or if it blows warm air when it's in cool mode), change the settings for the orientation of the heat pump.

O-oriented heat pumps would always call for heating since the O wire would constantly be deactivated.

B-oriented heat pumps would always call for cooling since the B wire would constantly be deactivated.

If the system continues to run, even if the Home app says the system is off, the reverse valve activation is likely set to seasonal instead of cyclical. Activating seasonally causes less wear on the equipment, but some heat pumps require cyclical activation.

Feel free to keep us posted if you have more questions.

Regards,

Gabriela

[PatrickJ2020]

It was set on O and I changed it to B.  I did notice cold air blowing the other day before hot air came.  Shouldn’t this be the case if B was selected? Do I need to do this every season change? Also why is this just now constantly happening and not before?

[GabrielaG]

Hi PatrickJ2020,

Thank you for keeping me updated. By default, the HVAC system is oriented as O or B. If your HVAC system operates in the B orientation, this configuration will be consistent throughout the year. Your system needs the B orientation regardless of whether you need heating or cooling.

Feel free to keep us posted if you have more questions.

Regards,

Gabriela

[PatrickJ2020]

Hello, my issue is not solved.  When our outside temps got above 37 and we went from the furnace to heat pump, it was blowing cold air.  I had to switch the wiring back to O in order for the heat pump to blow heat.  Propane furnace is back up heat below 37 degrees. My issue is not with the heat pump wiring settings.  Also it doesn’t make sense that I have been using this wiring setting for 5 years and this problem is just now occurring after I installed a new nest about a year ago.  Please advise on next steps.  I believe I need to file a warranty claim for a new nest.  Thank you for your help. 

[GabrielaG]

Hi PatrickJ2020,

Thank you for your reply. I appreciate your time performing the troubleshooting steps with me; I'm sorry to hear the issue is still not resolved. I'm happy to continue assisting you. 

We need to check if there is an issue with the backplate of the Nest Thermostat troubleshooting the OB terminal. If you feel comfortable, please follow the steps below.

• Turn the HVAC system power off through the breakers.
• Remove the Y1 and OB wires.
• Turn on the breakers and treat the system as a conventional heating system.
• Stop any call for heat or cool.
• Turn on the fan and verify if it activates.
• Put Y1 back, and swap the OB and G wires.
• Turn the power back on the HVAC system through the breakers.
• For heat pumps with O-orientation: Call for cool, but expect heat.
• Stop the call for heat or cool, turn on the fan, and verify if it activates.

Let me know how it goes.

Regards,

Gabriela