Yet another Nest Learning thermostat E77 error thread

[Marcus8983]

I'm installing Nest Learning thermostat (3rd Gen), just purchased from link.

I wired it as recommended by the Nest App (iOS) but it displays "Y1 wire not detected. Heat pump requires a Y1 wire. nest.com/e77". I neither have a heat pump nor an A/C; it just a single furnance.

I reviewed other people having the same issue:

1. Disconnect the the Y/O (yellow) wire from O/B (as suggested by Nest App) and connect to C. RESULT: No power connected (even though RH remains connected).

2. Disconnect the the Y/O (yellow) wire from O/B  and connected to Y1. RESULT: Y2 is required if Y1 is connected.

(This is frustrating on multiple levels. First, I'm having issues connecting this Nest. Second, I don't see an option to upload images in this community thread. I bought two Nests; both getting returned shortly if this is not fixed soon.)

[Patrick_Caezza]

@Marcus8983 

Post a picture of the original thermostat's wiring here.

[Marcus8983]

Hi @Patrick_Caezza ,

Thank you for helping me!!

I think the problem was in the existing setup, rather than nest: I have a single Furnace but with two zones: upstairs & downstairs. I have no A/C unit in the house, just heater. The blower and furnace are one unit.

This is the original thermostat connection UPSTAIRS.

And this is the original thermostat connections DOWNSTAIRS.

Please notice the Blue (C) wire is not used in either (upstairs thermostat, the wire is simply hanging, and downstairs thermostat, the wire is hidden into the wall).

Through numerous trial and error combinations, the connections that worked with nest for both upstairs and downstairs turned out to be:

Upstairs:

Downstairs:

Please notice how the Yellow (labeled Y/O) wire is no longer used and the previously unused Blue is now connected to C.

This combination has been working, ie, two independent zones that can be turned on or off simultaneously by two nest thermostats.

Here are the wires to the furnance

  
I just need confirmation that the combinations I did are valid (operationally, they seem to be valid since any other combination didn't work).

Thank you!!!!

[Patrick_Caezza]

@Marcus8983 

What is the heat source? Gas or Electric Furnace, boiler, etc?

Does each thermostat go to its own damper unit or does it go to a Zone Controller unit that is close to the furnace?

For a heat-only system, your wiring should work just fine. But the fact that the damper control is fully wired for both heat and cool makes me have questions.

[Marcus8983]

Hi @Patrick_Caezza 

What is the heat source? Gas or Electric Furnace, boiler, etc? 25 year old GAS furnace

Does each thermostat go to its own damper unit or does it go to a Zone Controller unit that is close to the furnace? Not sure what either mean. I can see the wiring goes directly to the furnace and I attached a picture of how the two cables are connected to the furnace. Is that sufficient to answer your question?

For a heat-only system, your wiring should work just fine. But the fact that the damper control is fully wired for both heat and cool makes me have questions.  Not sure! This unit was never intended or built to have an A/C unit; it rarely gets hot here if ever.

Thanks!