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Nest Learning Thermostat 2 Fan Speed Wiring

Community Member

My condo uses a heat pump system for both single stage heating and cooling. My current thermostat (ClimateMaster) has a low and high-speed fan option and uses both G and G2 wires. The online compatibility checker fails when I select the G2 wire but I'm aware that using Pro Mode to map the G2 wire to another connector such as Y2 seems to be a workaround. When I do this mapping, I get an error code of e113 which clearly states that G2 is mapped to Y2 and that's not allowed. Nest phone support just had me remove the G2 wire and suggested hiring a Pro Installer which seems unnecessary as the thermostat is already installed and functioning just fine w/o the G2 wire. Is there a workaround for the G2 issue?


Community Member

Anyone? No ideas or solutions from the community?

Community Specialist
Community Specialist

Hi diskman50,


Thanks for reaching out to us. We hear you. We're always looking for ways to improve and bring more features to our Nest Thermostat, such as having a workaround for G2 wires. We don't have anything else to share about its availability timeframe right now, but stay tuned for more news and updates. So, please let our product team know about it by sending feedback


In the meantime, I'll go ahead and lock this thread within 24 hours. If you run into any more questions in the future, please feel free to create a new thread.


All the best,


I need to know if other Nest customers have successfully installed a Learning Thermostat using the G2 (Fan) wire. I know that some users have mapped the G2 to Y2 as a workaround. However, if this is an impossible configuration, even for a Pro Installer, then I'll have to return the Nest and look for a different solution. 

Community Specialist
Community Specialist

Hello everyone,


Thanks for looking into this, Zoe.


@diskman50, to have your Nest Thermostat installed if your system includes several fan wires, get in touch with a Nest Pro. The thermostat or your system could be damaged by improper installation settings. Systems using G2, G3, GM, or GH wires, for example, require a Nest Pro to install them.




Hello diskman50,


I wanted to see if you still needed help. Please let us know if you have any other questions or concerns.



Hello Mark,

Thanks for following up on this issue. There has been no progress to date and it seems a little excessive paying for a Pro installation for a thermostat that is already installed and up and running except for the G2 wire (high fan speed) on my HVAC system. There have been a few posts concerning 3 speed fan installations but most of those lack a final conclusion by the author that the solution actually works. All I was looking for in my post was: 
1) Can the Learning Thermostat support dual fan speeds in a heat pump system (both Heat and AC)?
2) Can you map the G2 wire to Y2 w/o the Nest complaining about a wiring error? (this was attempted in Pro mode)
I was anticipating more responses other than hiring a Pro Installer.
Thanks again for the follow up.

Community Member

Is there a solution to this problem?  I think I just posted the same question regarding my climatemaster thermostat.  I have a g2 wire as well and I don't want to buy a nest if it won't work and would rather just install it myself as I've installed several before but without the G2 wire.  

I've discovered that if you have a heat pump, a wire in 0/B, you cannot map G2 to Y2 to get dual fan speed. The solution for me was to return the Nest and install a ecoBee Smart Thermostat Premium which supports the G2 to Y2 mapping with a heat pump. An added feature is that the Premium comes with an air quality sensor built in and a remote temperature sensor which is an extra expense on the Nest. The ecoBee is currently selling for $219 on the ecoBee website and at Amazon. 

As a side note Google's response to my problem was to hire a Pro Installer which would have been a total waste of money. I did hire my HVAC company to install the ecoBee though which was an added expense but worth it in my situation.

Regarding not using the G2 wire means only low fan speed will be used which in my situation allowed the AC unit to run a little longer thus removing more humidity from the room. However, in the winter months I want a high fan speed (G2 wire) to heat the room as quickly as possible. So not using G2 has some consequences.

Best of luck.

Community Member

Do you think you needed the professional to install the ecobee or could you have done it on your own?  David

Community Member

There were some settings that were different from the Nest regarding a Heat Pump reversing valve. Other than that, it was straight forward. There are YouTube videos that walk you through it.