Reversing valve not powering on dual fuel system

[ychromosome]

We have an issue whereby the Nest won’t power the reversing valve when it switches between our LP furnace and the heat pump in our dual fuel system.  It works fine if it just has to fire up the heat pump on its own, but if we have a cold morning where it’s using the furnace, but then later in the morning needs to use the heat pump, it never activates the reversing valve and instead blows cold air at us (even though it’s in heating mode).  It doesn’t have the issue any other time other than when it’s making the switch.  Our HVAC guy has confirmed in that scenario that there’s no power being sent down the O/B wire (and we know it’s set in the correct orientation).  Any suggestions, or anyone else seeing something similar?  To get it to actually blow heat at us, I need to be there to reset the Nest, and that’s not convenient at all…. 

[Houptee]

What is your Lockout or Breakpoint temperatures?

Read this article go to the section about Lockout temperature for dual fuel systems

https://support.google.com/googlenest/answer/9248719?hl=en#zippy=%2Cauxiliary-aux-heat%2Clearn-more-...

[ychromosome]

I have it set at 35 degrees.  System installer initially put it at 30, but I raised it a bit.  

[Houptee]

Do you have separate power wires?

Are there both RC and RH wires in this system?

Do you have a C wire?

[ychromosome]

There is no Rh wire, but there is an Rc wire and a C wire.  

[Markjosephp]

Hello there,

I'm sorry for any trouble this may have caused. Let's see what's going on.

@ychromosome, I found a helpful article with some troubleshooting steps for heat pump issues. Please let us know if that helps or if the same issue persists.

Thanks for helping here, @Houptee.

Thanks,

Mark

[ychromosome]

Thank you both for trying to help. Unfortunately, none of the suggestions on that page help.  The wire itself is fine, and the orientation is set correctly.  The Nest works well 98% of the time, it’s just when it has been running in ‘Alt Heat’ (LP furnace) and then needs to switch to normal ‘Heat’ (heat pump) because the outdoor temp hits 35 degrees (changeover temp) that the Nest fails to power the reversing valve.  It says it’s in ‘Heat’ mode but will blow out cold air until I manually reset the Nest.  After the reset, it properly supplies hot air from the ‘Heat’ mode.   

[Markjosephp]

Hello ychromosome,

Thanks for letting us know, and I appreciate the steps you've taken. Given that you had it reset to make it work, there must've been settings that needed to be configured. So we'd like to further look into this for you.

Please fill out this form with the needed information and let me know once you're done.

Regards,

Mark

[ychromosome]

Thank you Mark, I just submitted the form.

Also, I should have said that I need to "reboot" the Nest to make it work, not "reset" it.

Thanks!

[Markjosephp]

Hi ychromosome,

Got it! Thanks for clarifying and completing the form; we have received it. Soon, a member of our upper team will contact you via email. Also, please continue the conversation there, as this thread will be locked within 24 hours.

Best,
Mark

[Houptee]

Did you try going into the "pro setup" on the Nest and see what the settings are for the OB wire etc.

[ychromosome]

I'm not sure how to go through the pro setup, but individual tests of each of the systems shows that they work.  

[EdwardT]

Hi ychromosome,

I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further.

Thanks,

Edward

[ychromosome]

Hi Edward,

I was just contacted by a  Google Nest Customer Care Team member via email.  I have sent him a description of the problem and am hopeful this can be resolved.  If you want to work with me in parallel to me working with him, I'd be happy to do so because I want this resolved.  However, if you prefer to wait until we see if he can help me, then that works too.   Thank you for reaching out.

[ychromosome]

Hi All,

I wanted to provide an update to thank everyone for their assistance and to provide an answer for anyone else who may come across this.  I was contacted by a Google Nest Customer Care Team member who helped me walk through the problem.

The unfortunate answer is that the Nest will not work with my system; which is disappointing because I've enjoyed using it for years and I actually chose this system or a slightly more efficient one because my HVAC installer thought it would allow me to keep the Nest.  

I have a 6 stage dual fuel system (2 cooling, 2 heating via heat pump, and 2 heating via an LP furnace).  It ends up that the Nest can't handle the 2 stage heating from the LP furnace, it only allows for 1 stage auxiliary heat.  

Disappointing, but live and learn.  Thanks again for the assistance and hopefully this thread helps someone else who finds themselves with a similar problem.

[Jake]

Hey there,

I am sorry to hear that your system isn't compatible, but glad to hear you were able to get help. I am going to go ahead and leave the thread open for 24 hours in case you have any questions from here.

Best regards,

Jake