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Taco ZVC 406 Issue

bradstiff
bradstiff Member Posts: 7
My boiler is not responding to a call from my Indirect Hot Water Tank. The zone's yellow and red LEDs are lit on the ZCV. The override lever on the valve has no resistance when moving it to Manual Open, so it seems the valve is open. But the boiler end switch won't close. I measure infinite resistance across the end switch on the ZCV.

If I activate another zone via the zone's radiant heat tstat, the boiler end switch closes and both zones are heated. I can even deactivate the second zone, and the Indirect zone continues to heat until the Tstat is satisfied.

My valves are all 4-terminal Honeywell. When the red light comes on, I get a resistance that fluctuates around -0.5 ohms across leads 3 and 4 for the Indirect zone. If I jumper leads 3 and 4, the end switch closes and the boiler starts.

I have already tried moving the Indirect to another zone on the ZCV with the same result.

I think I need to replace the valve head; although it is strange that the ZCV indicates the switch is closed.

What do you think? Is it safe to replace a valve head? Is it easy to find a replacement online for just the head? It is a Honeywell Synchron (I can't find an actual model number).

Thank you.

Comments

  • HVACNUT
    HVACNUT Member Posts: 4,871
    Did you remove the wires from 3 and 4 and ohm out the wires themselves for the end switch on the zone valve.
    Your meter will probably read oL.
    Sounds like you need a valve head.
  • bradstiff
    bradstiff Member Posts: 7
    I did just now. Infinite.
  • bradstiff
    bradstiff Member Posts: 7
    The powerhead appears to attach to a brass plate, secured with two brass torx screws. The installation is about 12 years old. My understanding is I can just loosen the two brass screws and remove the powerhead and no water comes out. But I can't get it off. I can wiggle it some and twist it some, but that is it. Is there a trick to getting it off the valve itself?
  • HVACNUT
    HVACNUT Member Posts: 4,871
    The zone valve lever must be manually locked open to remove the power head. Twist and pull.

    If you can jump 3 and 4 on the board and the circulator starts, it's fair to say the zone board is good. If the valve is powered open and your reading 0 resistance testing the end switch wires, then it's fair to say the end switch is good.
    But one of them is not good otherwise it would work.
    Numbers on top or bottom of the power head? V84???
    bradstiff
  • bradstiff
    bradstiff Member Posts: 7
    Manually opening the valve did it. Came off easily. Switched the powerhead with another zone and now the Indirect is charging.

    It is V8043E1012
  • bradstiff
    bradstiff Member Posts: 7
    Noticed something on the bottom: "Motor compartment not to be used for field splices." Does that mean I am supposed to splice the wires outside the box itself? I am not sure what constitutes the "motor compartment." Is it the box itself? Or is it the cylinder that houses the motor?
  • HVACNUT
    HVACNUT Member Posts: 4,871
    That's the whole area inside the cover.
  • bradstiff
    bradstiff Member Posts: 7
    Uh oh, already made a splice there. What is the risk?
  • bradstiff
    bradstiff Member Posts: 7
    I made all four splices there.
  • Zman
    Zman Member Posts: 7,435
    I wouldn't worry about it. The end switches are rated for line voltage. Splicing 120 volts in the cover would be a bad idea, so the warning. With low voltage, not such a big deal.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    bradstiff