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Extra zone coming on with priority DHW

wt Member Posts: 13
Hi all, I'm not sure if our Taco ZVC 406 is fritzing out or what. Whenever our DHW (zone 6, priority on) calls, our zone 4 comes on. The box is 19 years-old but nothing has changed with it in terms or wiring or anyone doing anything with it or to it. I just happened to notice both zones on one warm day, so I tested it and sure enough, zone 4 calls whenever zone 6 calls. It appears as if zone 6 is causing zone 4 to call. Anyone ever seen something like this? Do I need to get a new Taco unit?

Thank you very much in advance,



  • wt
    wt Member Posts: 13
    No ideas yet? I'm a little surprised. Should I just replace the ZVC 406 and cross my fingers then?

  • Paul48
    Paul48 Member Posts: 4,469
    I'd say replace it. It's doing something, it should never do.
    HVACNUT Member Posts: 5,490
    If you remove wires from TT on zone 4 and jump TT on zone 6 and zone 4 valve still opens, it's internal and you need a new board.
  • Dave H_2
    Dave H_2 Member Posts: 535
    Start with the simple "testing" like @HVACNUT suggested. Each circuit should be separate.
    Isolate each zone and test one at a time.

    Dave H
    Dave H
  • wt
    wt Member Posts: 13
    edited March 2017
    Indeed - I jumped zone 4 TT to 6 TT and it again caused it to call. Will replace board. Thank you!