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No option for dual fuel/emergency/auxiliary heat

Community Member

Greetings community, hope someone can help with this strange setup. I have a single stage heat pump with a gas forced air backup for heat. Coming from a Honeywell VisionPro TH8320U thermostat. See the photo from the Honeywell wiring. 

PXL_20230813_220749168.jpgThe right side connections are: R, O/B, Y, G and C. On the left, only a jumper exists between Aux and E. There is a factory jumper between RC and R but you cannot see it. 

This thermostat wiring appears correct according to my brochure photo:


There was no L wire connected and there are no sensors. So without the jumper, there were only 5 wires. 

This is the way my nest is wired


 i seem to be missing a wire in the nest to activate the dual fuel/emergency/auxiliary heat option. Cooling is working fine now and I'm sure heat pump heat would also. There is a possibility that a white wire should have been connected to one of the E or Aux terminals on the Honeywell. That could then be connected to the nest. It may have been disconnected from the Honeywell when I opened it...? Thoughts??



1 good thing is that you have enough wires to set up as you want. Is there any wires connected behind that short yellow jumper between aux & E? If not then that jumper isn’t doing anything. Since you want to use the heat pump as the 1st stage of heating you have it set up correct on the nest base if you want to use the gas heat for 2nd stage heating you need to connect it to aux/w1 on nest. Normally you want to use gas heat as 1st stage & heat pump as 2nd stage idk how your set up is so not sure what to advise you. Where i am natural gas is usually cheaper than elec. so preference is gas 1st then electric heat / heat pump as 2nd stage plus if you furnace is acting as your primary air handling unit and have your AC / heat pump indoor evaporator coil install after the furnace your refrigerant temps & pressure are going to be thru the roof when system kicks in 2nd stage heating cause now you’re pushing gas heated air onto the heat pump indoor evaporator coil. Of course I’m guessing that’s how it is you might have separate furnace and air handler idk. Hope that helps good luck.   

Community Specialist
Community Specialist

Hello Wineshopper, 

Checking in — did you get a chance to try the steps shared by HVAC about the wiring configuration on your Nest thermostat? If so, how did it go? Let me know if you need more help.

Thanks for the help, @HVAC.