Nest Thermostat Wiring

[jgscuba1]

I just purchased a Nest Thermostat and it seemed to be working fine until today. I noticed I got a N260 error. I only have hot water radiators for heat. I have 2 wires at the thermostat. The red one is positive and the white is negative at the heater. I put the white wire on the W connector on the Nest and the Red wire on the R connector on the Nest.  How do I get rid of the error message?

[Houptee]

You have to connect a C wire to provide the constant power to the Nest.

Is there a spare wire in the thermostat cable coming out of the wall or is it only 2 conductor cable?

If you have a spare color you can use it as a C wire.

If no spare wire then you have 2 choices, go buy some 5 conductor thermostat cable and run a new cable to the Nest.

Or order a power adapter.

[jgscuba1]

I do have 24 volts AC coming to the thermostat on the 2 wires. What is a power adapter and how would I connect that?

[Houptee]

You need a C wire its the negative and R is positive so the Nest will have power all the time on R+ and C-

The W is the signal to turn on the heat.

Did you look at the cable coining out of the wall if there is a extra wire in that cable not being used?

That is the easiest way to fix the problem if there is already a spare wire.

If not the power adapter has to be wired to the furnace and the 2 wires that go to the Nest. It has special circuitry to supply the power thru the 2 wires.

I suggest that adapter as last resort if you cannot pull a new 5 conductor cable up the wall to the Nest.

Usually the old cable is not stapled in the wall and you can tie a new cable to the old one and pull it down from below or up if furnace unit is in attic.

[jgscuba1]

Hi Houptee, The wiring I have is one wire from 24v transformer goes to pilot control, then to temperature sensor. From sensor to 1 side of thermostat. The other side of thermostat goes to 24V transformer.  So how would I hook up power adapter with this setup?

[Houptee]

You never said if you have a extra unused wire in the cable going to the thermostat. Did you look at the thermostat cable and see if they snipped off any other wires with different colors or is it the old 2 wire only type thermostat cable?

[Houptee]

The wire from the transformer that goes directly to the Red on the thermostat is your R + and then the other terminal on the Transformer would be the C Common side.

If you have a extra wire in the cable connect it to the Common side of the transformer (NOT the screw that feeds Red + wire).

If no extra wire do you think you can pull a new 5 conductor thermostat wire to the Nest? They sell the cable at Home depot, Lowes etc in a bag of 25ft or 50ft.

If not then you need to order the power adapter and hook it up.

Watch this video

https://youtu.be/xlx2Um6D1Z8

[jgscuba1]

I do have a power adapter. So do I connect the R wire from the transformer to the R wire on power adapter? Do I connect the White wire from the heat sensor to the W wire on the power adapter? What wire do I connect to the C wire on the power adapter?

[Houptee]

If you have a extra wire going to the thermostat you don't need the adapter at all. You just connect it to the transformer C. 

If you want to use the adapter then you disconnect the R W coming from the nest and put them directly to the 2 wires R W on the adapter like in the video. 

Then the 3 wires on the adapter connect to the place you disconnected the R from. And the W goes where the W used to connect.

Then put the C to the transformer screw that you said goes to the sensors. 

[jgscuba1]

It looks like its working fine, thanks for all your help

[Houptee]

Oh nice you got it working!

Did you do the Power Status test?

Go to the Nest then Settings, Equipment, Power Info.

You should see Vin is voltage should be above 24v

Lin and PS C - should be the same number around 350 or more.

[Markjosephp]

Hello there,

You're a big help here, @Houptee. 

@jgscuba1, I wanted to ensure that everything was covered here. Please let us know if you have any other questions or concerns.

Thanks,

Mark

[Markjosephp]

Hi jgscuba1,

I wanted to see if you still needed help. Please let us know if you have any other questions or concerns.

Thanks,

Mark

[Markjosephp]

Hello jgscuba1,

I'm checking in to make sure that you've seen our response. Please let us know if you have any additional questions or concerns before we lock this thread in 24 hours. 

Thanks,

Mark