C Cable adapter compatible system

[Dmasi]

Trying to set up 2 nest thermostats with my Navien tankless heating system. While setting them up, I got the dreaded low power message. I was able to order the nest c-cable adapter and should arrive tmw. I looked up the heating only diagram to have an idea of how to connect it and wasn’t sure if I was able to use with my system. If any one can let me know if I can use the c cable adapter and what to do I would really appreciate the help i need it!

if I remember correctly I’m getting like 18v when I take a reading at the thermostat, I’m surprised that isn’t enough and still need to c cable. 

<a href="https://gyazo.com/867a51b2f05c35308a9084620c0db20d"><img src="https://i.gyazo.com/867a51b2f05c35308a9084620c0db20d.jpg" alt="Image from Gyazo" width="4032"/></a>

<a href="https://gyazo.com/d9ad689a73d30e34a41ba600ff461cbf"><img src="https://i.gyazo.com/d9ad689a73d30e34a41ba600ff461cbf.jpg" alt="Image from Gyazo" width="3024"/></a>

[CoolingWizard · Accepted solution]

@Dmasi ,

Yes, you may call it the C-Cable adaptor, Google calls this the Nest Power Adapter.  

AC Cooling Wizard

[CoolingWizard · Accepted solution]

@Dmasi ,

I just noticed that you have two unused conductors wrapped around the thermostat cable. One is Red and the other looks Brown. 

AC Cooling Wizard 

[CoolingWizard]

@Dmasi , 

hang on a second here. So what you’re trying to do is control Navien tankless condensing boiler? The problem you have is that the Navy and operates his control system with 120 V of AC power. There is no 24 V power available and the two terminals that activates the zone T and T are simply a signal that when T is connected to T it activates that zone.  
if you can provide me the model number of the boiler you have I can look up the installation manual and see if there’s a way to add a 24 V power supply for the thermostat in such a way that it will not damage the control board.  Also since this is a heating only application you really don’t need a learning thermostat the basic nest thermostat that uses a couple of AA batteries would be more than sufficient  

AC Cooling Wizard

[Dmasi]

Thank you for your reply. Here is the invoice for which Navy I got. 

<a href="https://gyazo.com/656895039643d98dcadbba7bc8bd33de"><img src="https://i.gyazo.com/656895039643d98dcadbba7bc8bd33de.jpg" alt="Image from Gyazo" width="430"/></a>

I’m getting 18v at the thermostat tho. Is that not sufficient enough to run the nest I have?

which is the basic nest that would need only batteries, I will probably just pick those up and return the others.

[Dmasi]

@CoolingWizard if you look at the top left of my control board, there is a 2 port terminal comm/24VAC is that what I need to use?

[CoolingWizard]

@Dmasi ,

on that case thank you for the clarification and you indeed have your 24 V you need you just have to have a power connector or install a new thermostat cable with five conductors. if you have three zones, you must have three thermostats and if they’re all nest thermostats, you will need three power adapters

AC Cooling Wizard

[Dmasi]

@CoolingWizard 

When you say power adapter do you mean the c-cable adapter? Or the wall plug in?

[CoolingWizard · Accepted solution]

@Dmasi ,

Yes, you may call it the C-Cable adaptor, Google calls this the Nest Power Adapter.  

AC Cooling Wizard

[Dmasi]

Okay thank you for all your help! I’ll let you know how it goes.

[Dmasi]

@CoolingWizard just want to confirm this is where I need to tie in the two power adapters? And the comm for both can go in the top left terminal.

[CoolingWizard · Accepted solution]

@Dmasi ,

I just noticed that you have two unused conductors wrapped around the thermostat cable. One is Red and the other looks Brown. 

AC Cooling Wizard 

[Dmasi · Accepted solution]

I forgot to attach photo to last comment! 
im sorry!

 

[Dmasi]

@CoolingWizard 

[Dmasi]

UPDATE: This is how I wired it with using (2)nest power connectors. I can confirm, both are success work powered and working.