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Taco ZVC 405

Rob L_3
Rob L_3 Member Posts: 25
Yeah, that popped in to my head as I was driving home. Lucky this is not an emergency. I will try that suggestion on Tuesday.

Rob L


  • Rob L_3
    Rob L_3 Member Posts: 25
    Taco Zone Valve Controller Question

    I have a Taco ZVC405 in the field with an odd problem I haven't seen before.
    This particular controller has 4 T-stats and 4 zone valves connected, with one zone pump and has worked great for about 7-8 years. The problem that just started today is that the zone 4 end switch activation will no longer turn on the zone pump. The yellow diagnostic light on the right hand side indicate that end switch is activated, but pump does not come on. Zone 1-3 end switch activates and then pump will turn on. I switched leads on valve and t-stat over to unused zone 5 connections and still get same symptom. Odd? Sure is to me. If anyone out there can provide some useful tips, it is greatly appreciated.

    Rob L
  • Rocky_3
    Rocky_3 Member Posts: 232
    just wondering

    If it is not a problem with the zone valve end-switch, even though it shows yellow activation light. Have you taken one of zones 1-3 and put on #4? I mean we know that they work, if all of a sudden you take one of them zones and put on #4 and #4 works, then you've eliminated the ZVC control. Just odd that the same zone valve doesn't work on either #4 or #5...what are the odds that both contacts bad? Try taking one of the ones that are activating the pump and put it on zone #4 and see what happens.
    Good luck,
  • just listening

    Not to kidnap your thread, but I have a couple of ZVC406's installed on a job in San Francisco; got a "no-heat" call to find the system pump was not working. Turns out that the end switch in the ZVC406 was not closing whenever any of the zones were calling for heat and had to switch the wiring to the "slave" ZVC.

    The job is about 3 years old.
  • Darrell
    Darrell Member Posts: 303

    The ZVC lights go to red when the end switch closes...if you only get yellow that indicates call for heat but not a fully open zone valve. If it is a Honeywell v8043 then it is only opening about 90% and not closing the switch...very common...be sure to rebuild the whole valve and not just replace the motor.

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  • Joe Mattiello
    Joe Mattiello Member Posts: 703

    The yellow light indicates a demand, and the red light indicates an endswitch closure. Apparently, thermostat's calling for heat, but the endswitch did not close. You can try taken the valve endswitch wires off, and placing a shunt between terminals 3, and 4 on the ZVC board. The endswitch red light should illuminate as soon as the yellow light illuminates, and the main endswitch will close energizing the boiler.
    Joe Mattiello
    N. E. Regional Manger, Commercial Products
    Taco Comfort Solutions
  • Rob L_3
    Rob L_3 Member Posts: 25
    Problem Solved

    I was getting both lights red and yellow. But for some reason that zone valve must have been giving a false end switch signal. I changed out zone valve motors and system is working as it should.

    Thanks for the tips.

    Rob L
  • Rocky_3
    Rocky_3 Member Posts: 232

    After reading this thread, went on a call last night with a ZVC 403. There were only two zones connected. Yellow lights on both on, only no red tail switch light. One motor was stuck at about 60% open, the other motor was completely open, but the little paddle that pushes the tail switch lever wasn't engaging the lever. Ergo, no activation of tail switch, and yes, they were Honeywell V8043's in a heavily glycolled system. Happens alot on the V8043 with glycol. One of the things I tell my guys on low heat calls, "Make sure the tail switch is actually engaging." Too often we just check the motors to make sure they are open without making sure each individual zone valve can turn the pump on by itself, without anything else calling. The dianostic lights on the ZVC make this easy to check now.
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