Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Taco ZVC Wiring

_ray_ Member Posts: 6
Hi Everyone,

I have a question regarding wiring a ZVC to a boiler that has built in DHW Priority (Triangle Tube Prestige Solo 175).

I have a ZVC 406-4 and am planning on using this in NON priority mode to be able to power up to 6 zones (4 currently in use). I would like to use the boiler's built in DHW priority switching so that I don't have to use one of the ZVC zones for DHW. In this case, how would the system circulator be wired?

The Taco instructions indicate the circulator should be wired directly to the ZVC, but it seems like this could end up ignoring the boiler's DHW priority control. Instead, I feel like I should only wire the temp relay from the ZVC to the boiler and then run the circulator from the boiler's circulator outputs. Is this correct? In that case, do I still jumper the 120v to the dry contacts on the ZVC or leave those contacts empty, only powering the relays?

Thanks a TON.


  • Zman
    Zman Member Posts: 6,975
    TT 175


    Just let the triangle tube drive. It has relays to control the both circulators. The only thing that needs to connect the boiler to the taco is the low voltage TT wire. You just have to configure the controller for your piping arrangement.

    I assume you have worked out the minimum flow requirements?

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • _ray_
    _ray_ Member Posts: 6
    Hopefully didn't shoot myself...

    Thanks (again) Carl for your input. Thats what I was thinking, but just wanted to be sure.

    After seeing your comment about the flow, I went back and reread my first post and it looks like I've missed something there. TT gives the minimum flow requirement only at high output, which is 8 gpm. Unfortunately, I don't have a low output number though, so I'm forced to speculate...

    Given that I'm using a dT circulator (bumblebee) and the boiler should modulate to a proper rate to match demand (which i can control better with the bumblebee) it seems that I shouldn't be approaching that maximum except on multi-zone or DHW calls. Of course, this is speculation though and I'm beginning to get a little worried that I've missed something on my setup (after rereading manuals and forum posts tonight).

    In my system, I have 4 zones with loads of 10k, 26k, 27k, 35k. A couple of these are pretty long runs since the new boiler is in the opposite corner of a split level ranch and feeding the addition on the other side. These are all piped direct using the Bumblebee, I'm setting a 30 degree dT as was previously suggested. DHW will be hooked up as I mentioned previously, tied to the boiler directly and uses its own Taco 007.

    Given this scenario, do I need to revisit my piping arrangement and convert to P/S? That would _really_ suck. Killing my boiler would suck more though.

    While we're on the topic of retrofitting a new system (and, the answer here may not matter so much if I must revisit P/S): When we talked before about the differential bypass not being an issue with the Bumblebee, one thing I didn't think of there (maybe others did) was post purge. I think that the ZVC will close the valves once the thermostat has been satisfied. At this point, the heat call is terminated, but the boiler has a post purge set up. Do I need a bypass in place and tuned such that it allows flow when NO zones are calling? This should allow clearing the heat exchanger at least...
  • SWEI
    SWEI Member Posts: 7,356
    edited October 2013
    Minimum flows

    Given that the TT 175 modulates from 50k-170k, the 8 GPM minimum flow rate would drop to roughly 2.4 GPM at low fire.

    What you are seeing is a demonstration of the problems merging bang/bang zone control with ODR.  Using TRV for small zones will minimize (or often eliminate) the issue.
This discussion has been closed.