Honeywell to Nest Wiring

[ChrissyF]

I am trying to wire my new Nest Gen3 .  I had an old Honeywell thermostat. With the old Honeywell there were only 4 wires in use: a red and white attached to one screw and a blue and white wire attached to the other screw.  I have an old oil burner.   No heat pump, no a/c.  I have tried every combination of wires and the thermostat constantly says that it’s out of power and must shut down.  I’m really at the end of my patience with this.  Can anyone help?

[sporfrog]

It would be helpful to attach a photo of the wiring block on your old/existing thermostat with the wires attached.

[CoolingWizard]

The contractor that installed your system did not use a proper thermostat cable. They used a telephone cable that’s why the wire coding colors are blue with a white stripe, and Red with a white stripe. You heating system has only two wires, The R and the W.  So one of the wires was on the R or Rh, and the other was connected to W. 

Connect the one that was on the R or Rh to the nest Rh, connect the other one that was on the W to the nest W1.

The AC Cooling Wizard

[ChrissyF]

Tried that wiring and still no power to Nest and the burner doesn’t go on.

The only way it turns on is when the white and red are put in together in either the Rh or W1 

Theres a junction box for Honeywell outside the main electrical box in the basement with split wiring….. white/green and white/blue.

This whole system of wiring in this house is so antiquated!

[CoolingWizard]

Part of the problem that might be is the contractor used 22 gage wire and thermostat wire is 18 Gage. If the wire run is to long, there can be to must power loss. Additionally, some systems that are heating only have gas valve that do not operate in 24 V system. They simply have two terminals label TT and all that is needed to turn on the heat is a connection between the two. A basic thermostat will do that the nest can do that, however, the nest learning thermostat needs a common wire and 24 V line wire in order to keep the battery charged.

The AC Cooling Wizard

[Markjosephp]

Hello folks,

I wanted to ensure that everything was covered here.

Thanks for the help here, @sporfrog and @CoolingWizard. 

I hope you've got the answer you're looking for, @ChrissyF. I found a helpful article to identify a thermostat wire that might help with your compatibility checking. If you're still in need of assistance, feel free to let us know.

Regards,

Mark

[Jenelyn_O]

Hi there,

I wanted to follow up if you still need help. Please let me know if you’re still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

I appreciate your help, @sporfrog, @CoolingWizard, and Mark.

Best,
Jenelyn

[Jenelyn_O]

Hello there,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns, as I'll be locking this thread in 24 hours.

Thanks,
Jenelyn