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I have a nest with 3 wires. Red/Black/White

Rbrady
Community Member

I have a nest system hooked up with two zones for my boiler. The upstairs is the main controller with the nest hooked up. There are three wires: black, white and red. The red is hooked up to the w terminal and the black is hooked up to the power terminal. The white is tucked behind. My system is overrunning sometimes. Is this hooked up correctly?

9 REPLIES 9

CoolingWizard
Platinum Product Expert
Platinum Product Expert

How were the wires attached to which labeled terminals on the old thermostat? Can post the picture you took of the old thermostat backplate with the wires attached.? Can you provide the make a model number of your furnace? 

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

The thermostat is operating a Weil-McLain CGA5SPDN Boiler.

PXL_20230324_235315495.jpg

The White wire is taped and shoved back into the system.

Unfortunately do not have pictures of old thermostat. It has operated correctly 95% of the time. Just overheated once or twice a year for the last 4 years, and now this year it is doing it almost once every other week.

CoolingWizard
Platinum Product Expert
Platinum Product Expert

0237DF83-C871-4473-A4BF-0D1E36227280.jpeg
This is from the installation manual for your Boiler. If you know, I put a yellow box around the location where you can find both the R and the Common in that control board. 

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Hell folks,

 

I wanted to ensure that everything was covered here.

 

Thanks for the help here, @CoolingWizard,

 

@Rbrady and @yanrubin, I hope you've got the answer you're looking for. If you're still in need of assistance, feel free to let us know.

 

Regards,

Mark

Juni
Community Specialist
Community Specialist

Hi there,

 

I'm jumping in to follow up if everything is good here. Let us know if you have any further questions.
 

Thanks,

Juni

Rbrady
Community Member

Yes, 

I believe it is hooked up correctly. The Nest works perfectly.

Markjosephp
Community Specialist
Community Specialist

Hello Rbrady,

 

Sounds great! Thanks for the update that your Nest Thermostat is up and running. So I'm going to lock this thread in 24 hours. If you have any other concerns or questions, please feel free to create a new thread.

 

Regards,

Mark

yanrubin
Community Member

Not sure it may help but I had looks like the same problem. I have an older generation unit which I am able to set up using it's menu. It was set up but didn't want to work with dual zone system. What I found that the heater system wasn't able to provide enough current through special dual zone PCB. You may be able to find out with menu H/W check that the current in 10ths MA. The connection cable has more unused wires which one can use to add the GND connection. Add it to PCB output connector and to Thermostat input connector. The current rose to around 85mA and thermostat began properly working after. I actually tried to use use live Support but -they had no idea about such issue when Dual Zone adapter is used.

Hope it may help you.

CoolingWizard
Platinum Product Expert
Platinum Product Expert

The best way to ensure proper charging current is to use a power COMMON wire.  Your boiler uses 24VAC control power, then the power common is possible.  

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.