# Wiring Indirect Hotwater heater thermostat to condensing boiler with its own control?



## johnds1 (Dec 2, 2013)

Hey guys,

I am a little confused and I need some help. I had just installed a condensing boiler. Everything went smooth. This particular condensing boiler(not sure if all of them are like this) has its own control panel(line voltage and low voltage) which there is no need for an external Taco SR504 unless of course you have more circulators than what is here. The line voltage terminal bus receives 120v power for boiler and also distributes 120v power to circulator pumps(in this installation: boiler loop circulator, heating zone ciculator, and indirect water heater circulator).

The low voltage terminal bus has two terminals each for: Heating t-stat, DHW temp switch, outdoor sensor, header sensor, remote firing rate, and external limit. 

My problem is this. I am using the old indirect water heater. It is a Vaughn Top Performer Plus. The thermostat for it is the one with the temperature and differential. It has 4 terminals(two terminals on each side). 
One set of terminals read: pump/TT
Left termainal labeled NO and right terminal labeled COM

The other set of terminals read: 24v ac/dc
Left terminal labeled Hot and Grnd

How is this hooked up if boiler is controling everything and only has two terminals for indirect t-stat? I under stand that some indirects have just a two terminal t-stat, but how can i make this work? Thanks guys. Sorry for the lengthy question but i wanted to be as clear and thorough as possible. Here are some photos:

Indirect Water Heater T-Stat








Internal Boiler Schematic


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## johnds1 (Dec 2, 2013)

Double post, sorry. Thank you for any help guys.


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## beenthere (May 30, 2009)

By now I'm sure you figured it out. but that control would need to be supplied with 24 volts from the boiler's transformer. By connecting the hot and ground terminals to the boiler's transformer. Then connect the NO and COM terminals to teh boilers DHW terminals.


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## johnds1 (Dec 2, 2013)

beenthere said:


> By now I'm sure you figured it out. but that control would need to be supplied with 24 volts from the boiler's transformer. By connecting the hot and ground terminals to the boiler's transformer. Then connect the NO and COM terminals to teh boilers DHW terminals.


Yes, all is well. Thanks anyway for posting just in case i hadnt figured it out lol. It is wired just how you explained. I had to call boiler manufacturer to see what terminals I can jump off the boiler for a constant 24v. 
I was thinking about getting the Nest thermostat for my living room. Do you have any experience with that as far as that needing a constant 24v supply as well? If it does, i am wondering how it would be wired because I also have a separate central a/c system that will be connected to it. I was concerned about this because which system would supply the 24v, boiler or air handler, and i dont want to backfeed one or the other.


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## beenthere (May 30, 2009)

No experience with the Nest myself. Just read of lots of problems with them.

Might want to check out the Ecobee. 

Usually powered off of the heating unit.


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