Upgraded from Gen 2 to Gen 4 thermostat, hot air blows cold / N407 error

[FRAH0709]

upgraded from gen 2 thermostat to gen 4 , copied old wiring to new and now I do not have hot air. Previously (2nd gen), did not have OB wire connected before ( only Y1,G,W1,*,Rh) and now heat is blowing cold air / N407 error. I tried re-installing app and it auto detects the OB wire as well?  I am totally at a loss here.

For * I have a blue wire, not sure what it does ; shall I try to use for C (common) or OB?

Here is old set up (gen 2, brown wire) , new set up, error, detected wires ( I have no OB!)

https://imgur.com/a/2BDplC6

https://imgur.com/a/2BDplC6 

[ByronP]

Hi FRAH0709,

Thank you for reaching out to the community. I see you're experiencing trouble with the wiring configuration for your Nest Learning Thermostat (4th gen) after upgrading from the Nest Learning Thermostat (2nd gen), I understand that this is giving you an error code N407 and that the heating doesn't work, you're only getting cold air. I appreciate all the troubleshooting steps you've already taken as well as the detailed information and pictures you provided. I'm glad to help.

To provide better assistance, please answer the following questions:

• Did you install the thermostat yourself?
• Does the thermostat screen indicate that it’s actively calling for heating?
• What type of HVAC system do you have? (Conventional, Heat Pump, etc).
• Have you recently experienced a brownout or blackout?

Additionally, here is a helpful article to identify the wires for your Nest Thermostat so you can clearly check the ones you set up and review which type of wire you have.

Please keep me updated on your findings.

Regards,

Byron

[FRAH0709]

Thanks for your help!

I found a work around to make heat work , by using option “use emergency heat”

but looking for long term solution still!

• Did you install the thermostat yourself?-—-Yes the 4th gen , but 2nd gen was by nest pro 
• Does the thermostat screen indicate that it’s actively calling for heating?
  — it would turn on then turn off within minutes before I used “emergency heat” option, when it did work it only blew cold air
• What type of HVAC system do you have? (Conventional, Heat Pump, etc)-— —traditional gas furnace 
• Have you recently experienced a brownout or blackout?
  —no HVAC is only a few months old

[ByronP]

Hi FRAH0709,

Thank you for your prompt reply. I appreciate the detailed information.

Based on your answers, please try these recommendations:

Step 1: Check the Blue Wire.

• In the previous wiring information, you connected the blue wire to the terminal marked with an asterisk (*).
• Please ensure and take a picture of the panel control for your gas furnace where this wire originates. This is to confirm if the blue wire is indeed a "common wire" so you can move to the "C" terminal where the wire needs to connect.

Important Note: Before you check any wires or perform any reviews, please turn off the breakers.

Please let me know how it goes.

Regards,

Byron