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How to wire zone controller with existing transformer relay

KirkbeeKirkbee Posts: 8Member
I'm having an issue with wiring my Weil McLain gas boiler. It was wired up fine and working for a single zone. I added (2) 4 wire zone valves in. So I now have 2 zones, a Taco zone valve controller(zvc-403), and two ecobee thermostats. And I have no idea how to wire it up.

I watched a video that showed me how to wire the valve controller. By wiring the circulator to the pump end switch and each of the thermostats to the proper zone and each zone valve to the proper zone on the board. That was pretty self-explanatory. But my question is: What happens to all the other connections on the boiler?? Like the water limiter and the gas wiring relays etc. I currently have a transformer relay with a lot of wiring connected to it - and no idea what to do with all those connections.

Do I just take the thermostat wires off the existing relay transformer and connect them in the controller and bring 120V to the controller to power it, and leave those connections powered with 120V to work completely on their own as long as it has power?

Or do I remove the thermostat wires from the existing relay transformer and bring the them to the controller, and remove the 120V power fro the existing relay transformer, and run the thermostat wires through the relay transformer as they were before? So no power in that relay transformer.

Or do i connect wire from the isolation end switch ti where the thermostat connections were made on the transformer relay

They completely left out what to do with all these other existing connections from the transformer relay. What about the gas igniter and the high water limiter etc. . Can anyone help with this? I have a decent idea of electrical work just never worked with HVAC and relays.


  • HVACNUTHVACNUT Posts: 2,868Member
    Listen, sit down, take a breath.
    Now go to the top of the page and click on find a contractor in your area.

    Where are you located and can you post some pics?

    No offense, but you write, "I have no idea where this goes." "I dont know what that does." "What do I connect here."

    This says to me that you definitely need a heating pro to check, repair, rewire, combustion test, to make your system safe, especially if your not positive on the proper wiring of a gas burner circuit. And he'll take a look at those "controllers and limiters " too.

    Kindly shut off the emergency switch and the gas valve, and check for contractors here.

    Now you can relax and grab a coffee.
  • hot_rodhot_rod Posts: 12,590Member
    the relay box should have a wiring schematic. As long as you didn’t unwire anything in the boiler a simple connector from the relay to the boiler TT should control the booker as before
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • TitanMechNYTitanMechNY Posts: 2Member
    I agree with hot rod. As long as you didn’t touch anything besides the existing t-stat wires, all you would need to do is run the end switch from the Taco to where your old t stat used to connect (usually labeled T-T). For the 120v I usually pig tail off the emergency switch to feed the boiler and Taco box so everything goes off when you hit the switch. Good luck.
  • KirkbeeKirkbee Posts: 8Member
    edited October 2018
    Thank you. I havent disconnected anything. My boiler still works as if it used to when i manually open the zone valves

    The transformer relay has everything wired up and has been working safely. That was done by a person who serviced the boiler previous to me. So all of that is good to go. I wont take any of if apart, which i didnt plan on doing in the first place. And just terminate wires from the pump end switch to where my tstat wires are on the relay transformer. That should signal the boiler to work just the way it was when the tstats call for heat. Correct?
  • KirkbeeKirkbee Posts: 8Member
    Here is a pic of what it looks like. The red and white are my t stat wires and blue is my common for my ecobee
  • TitanMechNYTitanMechNY Posts: 2Member
    If you added a zone valve and a t stat, both t stats and zone valves should go to the Taco box. The common for your t stats will come from the C on the terminals in the box next to the R and W. The X X would go to where the old red and white from the t stat used to go on your boiler. You shouldn’t be getting a common from the boiler circuit at all once the taco is installed.
  • KirkbeeKirkbee Posts: 8Member
    Copy. I got it. The common is in the picture and goes to the boiler because i havent taken it apart yet. It was to power my ecobee smart thermostat before i needed to add the taco box. Now that i added the zone and got the taco box. I will be doing exactly what u just mentioned. Question for curiosity. Pump end switch is marked XX Also the isolation end switch is marked XX. What are the differences?? I will be using the pump end switch tho
  • SteveSanSteveSan Posts: 47Member
    The pump end switch is just a dry contact for your circ. pump and the isolation end switch is also a dry contact to your boiler aquastat relay. Don't forget when wiring power to the zvc to run a jumper off the hot line down to one side of the pump end switch. Any questions please feel free to call into Taco Tech Support 401-942-8000 and ask operator for tech support.
  • KirkbeeKirkbee Posts: 8Member
    so wait. Now that confused me. If im gonna run red and white from the pump end switch to my where my existing tstat connections were. Which side of the pump end switch am i bringing a hot jumper too??
  • The isolated end switch (when connected to T-T on your boiler) will tell the boiler to come on. The pump end switch will tell your pump to come on.

    Study this diagram:

    You can see the Taco box is separated by a flat plastic divider. Above it is all your low voltage wiring. Below it is all your line voltage wiring.

    If you're not sure about anything, take HVACNUT's advice and call in a professional.

    Often wrong, never in doubt.

    Click here to learn more about this contractor.
  • KirkbeeKirkbee Posts: 8Member
    Does this look like its correct?
  • KirkbeeKirkbee Posts: 8Member
    And forgot the hot leg from the 120v power source to the first terminal of pump end switch
  • Yeah, you've got it.
    Often wrong, never in doubt.

    Click here to learn more about this contractor.
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