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Nest wiring problem

RobinHooD_ex
Community Member

I recently bought a house and tried to change 2 old thermostats for Nest.

At first, I got only 2 wires (pic.1), so I connected them and everything worked fine.

But at the second one I got 2 and 3 wires (pic.2). 2 wires (white and red) apparently don't work (I tried to connect them, but nothing happens). When I connect green and black, I can see a spark, and the Heating begins to work. but when I connect black to W and green to R, so it can turn on the heater, but I got "No power" error. (and Wi-Fi doesn't work besides energy drain)

Any suggestions how to connect it right ?

pic 1pic 1pic 2pic 2

 

10 REPLIES 10

Houptee
Silver Product Expert
Silver Product Expert

In the first pic it looks like you have a space wire wrapped around the cable. I suggest you use that for a C wire and go to the heating system and locate the C common terminal and connect it there. The Nest non learning needs a C for 2 wire systems or it will probably drain the batteries.

The second one I need to see a pis of the old tstat the way it was wired.

Is the second one also controlling a central AC system that might be what the other wires are coming from.


Houptee -- NJ Master HVAC Licensed Contractor

Unfortunately, I don't have a picture of the old one, it was removed during renovations.

There is no problem with Pic 1, I didn't notice any battery drain (but have n260 error on nest).

I don't have central AC, only a heater. 

 

Houptee
Silver Product Expert
Silver Product Expert

What kind of heat is this?

Is this a boiler with radiators or baseboard?

You said when you touch Black and Green the heat comes, on so put black in R and green in W.

Do not connect the other wires.

I would need pics of the equipment showing where the thermostat wires connect to the equipment to figure anything else out.

N260 code means C wire is required for the Nest.

So since you have some extra wires at each Nest go to the equipment and take very clear pics so i can help you figure out where the C common is and you can hook up a C wire for both Nests.


Houptee -- NJ Master HVAC Licensed Contractor

It is boiler with radiator. 

I tried black in R and green in W, heating working, but got "no power" error.

I have extra only at second, at first one everything is working fine.

Houptee
Silver Product Expert
Silver Product Expert

The 2 wire systems need a C wire or they do not get enough power to keep the Nest up and running and your wifi will probably stop working and batteries will die.

Need pics of the boiler wiring to figure out if you can put 2 power adapters on each Nest but they require a C wire connection at the boiler to work correctly.


Houptee -- NJ Master HVAC Licensed Contractor

I connected the green wire to C for pic.1 - still have an N260 error message. Can't get to the boiler wire box, it's very messy there. 

Houptee
Silver Product Expert
Silver Product Expert

The wire has to be connected to the Common side of the transformer at the boiler for the C wire to do anything.

You need to go to the boiler to see if you have zone valves or do you have 2 circulator pumps that have a control box for each pump?

There is no way to figure out where to connect the C wire without seeing pics of where the wires connect at the boiler.


Houptee -- NJ Master HVAC Licensed Contractor

aatienza
Community Specialist
Community Specialist

Hey RobinHooD_ex,

 

Checking in — we hope you've got the answer you're looking for. Let us know if you have more questions in mind.
 

I appreciate the help, Houptee.

 

Thanks,

Archie

aatienza
Community Specialist
Community Specialist

Hey there,

 

I just wanted to follow up to see if you still need our help. Please let us know as we would be happy to answer any questions you may have. 
 

Thanks,
Archie

No, unfortunately, it didn't work. I think it's better to call an HVAC specialist to fix it. Thank you anyway.