topic Wiring for the Nest Learning Thermostat Dual Fuel in Nest Thermostats

Wiring for the Nest Learning Thermostat Dual Fuel

tnikit — Sun, 02 Jun 2024 05:41:35 GMT

I have a dual fuel system. Heat Pump for heating/cooling and furnace for auxilary.

I've hooked up my thermostat and I've had Google support help walk me through it. Everything seems to be working properly except, I notice that the hear pump unit fan blades spin slowly continuously even though the thermostat is set to off.

My furnace circuit board has the following wiring:

R (red wire)
W/W1 ( white wire)
W2 ( black wire)
Y/Y2 ( orange)
G (Green)
O/B (Blue)

My old thermostat was wired as:

B orientation
O/B (blue wire) to O/B
R (Red wire) to R
Y/Y2 (orange) to Y
G (Green) to G
W2 (Black wire) to W2
W/W1 (white wire) to E

My wiring for the nest learning:

O/B (blue wire) to O/B
R (Red wire) to Rc
Y/Y2 (orange) to Y1
G (Green) to G
W2 (Black wire) to W2
W/W1 (white wire) to *

Does anyone see an issue with my wiring

Re: Wiring for the Nest Learning Thermostat Dual Fuel

alejandom — Thu, 06 Jun 2024 06:28:08 GMT

Hi @tnikit,

First I would like to thank you for posting in our community page, on the other hand I apologize for the inconvenience that you are having with your Thermostat. Let me tell you some troubleshooting steps that you can try to fix the problem.

There might be a potential issue with your Nest Learning thermostat wiring for a dual-fuel system with a heat pump and auxiliary furnace based on the information you provided. Here's why:

Missing Wire: In your Nest wiring, the W/W1 (white wire) doesn't have a corresponding terminal mentioned. Ideally, for a dual-fuel system with a Nest Learning thermostat, the W/W1 wire (often labeled as "W1" or "Stage 1 Heat") should be connected to the W1 terminal on the Nest.

Here's a breakdown of the typical wiring for a dual-fuel system with a Nest Learning thermostat:

R (Red wire): Connects to Rc on the Nest (common power)
O/B (Blue wire): Connects to O/B on the Nest (reversing valve)
Y/Y2 (Orange wire): Connects to Y1 on the Nest (compressor for cooling)
G (Green wire): Connects to G on the Nest (fan)
W2 (Black wire): Connects to W2 on the Nest (auxiliary heat, typically furnace)
W/W1 (White wire): Connects to W1 on the Nest (first stage heat, typically heat pump)

Possible Cause of Fan Running Continuously:

The continuously spinning fan on your heat pump even when the thermostat is set to "off" might be because the Nest doesn't detect the W1 connection (the first stage of heating, typically the heat pump). Without this connection, the Nest might be confused about the state of the heating system and keep the fan running for circulation purposes.

If for some reason you still have the same problem don't hesitate to let us know and call our customer service line for further assistance

Regards,

Mario.

Re: Wiring for the Nest Learning Thermostat Dual Fuel

tnikit — Fri, 07 Jun 2024 13:53:03 GMT

So I tried connecting the w1 wire (used to be on E on the old thermostat) to my w1 on the nest thermostat and w2 from old to w2 on nest. But I got an error saying that there's duplicate heating issue. Also w1 wire is my furnace so technically would I need to put this to w2 on the nest, and then put the w2 wire from old thermostst to w1 on the nest?

Re: Wiring for the Nest Learning Thermostat Dual Fuel

tnikit — Fri, 07 Jun 2024 13:54:12 GMT

Re: Wiring for the Nest Learning Thermostat Dual Fuel

alejandom — Sun, 09 Jun 2024 17:35:10 GMT

Hi @tnikit,

First I would like to thank you for posting in our community page, on the other hand I apologize for the inconvenience that you are having with your Thermostat and for the long wait. Let me tell you some troubleshooting steps that you can try to fix the problem.

You're on the right track diagnosing the wiring for your Nest Learning thermostat in a dual-fuel system. Here's why you might be getting the "duplicate heating issue" and how to address it:

Duplicate Heating Issue:

The error message likely pops up because the Nest detects two wires connected for first-stage heating. In your current setup:

W1 (white wire) is connected to W1 on the Nest (meant for heat pump)
W2 (black wire) was previously connected to W2 on the Nest (meant for auxiliary heat, typically furnace)

The Nest might be interpreting both connections as "first-stage heating," causing the error.

Correct Wiring for Dual-Fuel System:

For a dual-fuel system with a heat pump and auxiliary furnace, the typical wiring for the Nest Learning thermostat is:

W/W1 (white wire): Connects to W1 on the Nest (first-stage heat, typically heat pump)
W2 (black wire): Connects to W2 on the Nest (auxiliary heat, typically furnace)

Resolving the Issue:

Here's how you can fix the wiring and avoid the duplicate heating error:

Swap W1 and W2 connections: Move the W1 (white wire) from the W1 terminal on the Nest to the W2 terminal.
Leave W2 (black wire) connected: The W2 (black wire) should already be connected to the W2 terminal on the Nest for your auxiliary furnace.

Regards,

Mario.