Nest install woes


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Old 11-09-12, 12:54 PM
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Nest install woes

Hey guys,

I've had the Nest for a few months, but was only using cooling. For some reason I can't get the Nest to control heating properly. I live in a building with 9-units, with 1 boiler room shared by all.

Here's how the original thermostat was wired:



When I installed the Nest I saw that there was no way of connecting both C-wires, so I called Nest support. They told me to connect only one of them which should take care of it. I connected the white wire. It did make it work for cooling, but it reported no power on the W1 wire. Since I knew the boiler's for the heating system weren't running at the time, I thought that would come back up once that was turned on. It never did.

I called Nest to try and fix it, and they asked me to try the other C-wire. Didn't work. Then to try no C-wire at all. When we did that, I lost power to the Rh wire. Nest sent me a new unit that I received today, because they think I might have fried my unit somehow. All the other apartments in my building have the original Honeywell thermostats, and are working without any trouble.

I have a few questions for you guys. First of all, why is the original setup with 2 C-wires? What does that do? Secondly, how should I connect the new Nest? Is there a way of figuring out what's going on with those 2 C-wires and the W1 wire with a multimeter? What kind of voltage should be coming through those wires?

Thank you so much.
 
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Old 11-09-12, 06:32 PM
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I'm processing the wiring. Question.....I see two red wires connected. Can you tell us what colors are in which cable ? To clarify.... one cable with red, black and white wires. Second cable with red, green, yellow, etc.
 
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Old 11-09-12, 07:19 PM
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The second C probably serves the hot water valve.

Connect both C wires to an additional piece of wire with a wire nut and connect that wire to the stat C terminal.
 
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Old 11-09-12, 07:37 PM
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That would be like connecting two different units together with two different transformers.
 
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Old 11-10-12, 06:55 AM
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That would be like connecting two different units together with two different transformers.

Not if W is connected to the valve.
I work in high rises with boiler water and chill water and see this almost every day.

Running the actuator C to the stat instead of the air handler is a little odd though...
 
 

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