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Control wiring of older Taco zone valves

Mike M
Mike M Member Posts: 34
I dont understand how two different 24V power sources intermingle connections. The taco gold series zone valve gets power from an independent 24V transformer, This connects to a T87 then to Term 1. Terminal 2 goes to the return side of the transformer, AND it also connects to one of the TT terminals of a transformer circuit on the aqua stat. These are not dry contacts. The terminal 3 goes to the other TT terminal connection. The Burnham IOM says to check for cross phasing of the two transformers. It doesn't explain how to perform this check. Also, The L8148E doesn't have TT terminals. It has T,TV, Z,W...... so, which ones are the TT terminals, and how do I check for cross phasing these transformers??????


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,132
    edited January 2020
  • Mike M
    Mike M Member Posts: 34
    my question is more based on taco zone valves using two transformers and the #2 wire going to both transformers...
  • Mike M
    Mike M Member Posts: 34
    what are they talking about cross phasing the two transformers, the correction is to swap the two primary leads on the zone valve transformer.... its just how can I tell with my meter the proper connection without having to let out the smoke
  • Zman
    Zman Member Posts: 7,446
    If hot to hot is 48 volts, you have 2 phases in play.
    The easy way to deal with those is to install a zone controller and isolate it all. https://www.supplyhouse.com/Taco-ZVC405-4-5-Zone-Valve-Control-Module-with-Priority
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • JHK
    JHK Member Posts: 16
    The picture and the information below are taken right from Taco. T terminals go to 2 and 3. Common from the dedicated zone valve transformer also goes to terminal 2 and terminal 1 is W off the thermostat because R is being fed from the dedicated zone valve transformer.
    The following is copied right from Taco. While two circuits, each with its own transformer, touch at terminal #2, they do not communicate or interfere with each other in any way. Each circuit flows only in that circuit. This occurs because the transformer in either circuit cannot cause a voltage or current driving force to be realized in the other circuit when joined only at one point to that circuit.
    If you google Taco 3 wire zone valves you can get some links to YouTube videos and more literature.