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Second stage heat (w2) not showing voltage at furnace

Community Member

I just wired my Nest Learning Thermostat to my 2-stage furnace.  While doing the built in test on the Nest to verify function, I cannot get the 2nd stage heating to work properly.  Single stage (1st stage) works properly.

At the furnace, in first-stage testing, I see voltage at the W1 wire.

When I start the second-stage test, I still see voltage at the W1 wire, but no voltage at the W2 wire.

In an attempt to see if it was affected by the built in algorithms in the Nest, I left the 2nd stage heat test run for 15 minutes to see if it eventually kicked in the W2 voltage... but there was no change and the W1 wire remained high and the W2 wire sill showed no voltage.

Neither the Nest built in test nor then furnace show any error codes.

Removing the W2 wire from the nest connection allows the system to run as a single-stage heated (as expected), but it would be nice to get full functionality from the system.

Any ideas?


Community Specialist
Community Specialist

Hi rkrohn,


Thanks for reaching out and for being a step ahead of us. I'd like to take a closer look at it. A few questions: in what country are you located? What is the make and model of your heating system? What is your Nest Thermostat power readout? Please share with us the photo of the wires connected to your system's control board. Ensure that the labels of the wires are visible. Also, which voltmeter did you use to check the voltage from your wires? 


You can follow the guide below to check your thermostat's power readings:


  1. Go to your thermostat Quick View menu.
  2. Go to Settings.
  3. Look for Technical Info.
  4. Select Power.