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Quick question about Circulator wiring Weil Mcclain 97+

Sheepman24Sheepman24 Member Posts: 5
I have a condensing gas boiler that has control and end switches for DHW and 2 other heat zones. call for heat from low voltage terminal block inputs modulates boiler firing and circulation pumps for each of those zones with dedicated 120v terminals. DHW has priority settings from the boiler controller.

I am using only the DHW and one heating zone that is split into 4 zones controlled by taco 4 zone valve control.

The boiler is setup to output voltage for the heating circulator when a call from thermostats. But my taco also has 120v output for this pump? I feel like the solution to this is really simple but i cant find a definitive answer in my research.

I thought that in my case the circulator output was to supply voltage to the taco because in the manual it says as follows:

Use zone 2 output to:
a. provide 120v to system circulator(such as on a zone valve system with system circulator
b. provide 120v to a zone circulator
c. provide 120 v to a relay coil with relay contact used to enable/disable another device

i thought that option c was what i was looking at, but i cannot find a setting to change that makes the boiler treat that output as anything other than a pump.

Does anyone have experience with this, or know the solution?

Thank you in advance!


  • ZmanZman Member Posts: 4,855
    It really depends on how you have it piped. Do you have a drawing or pictures.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Sheepman24Sheepman24 Member Posts: 5
  • ZmanZman Member Posts: 4,855
    It looks like the heating side is direct piped with a pressure differential bypass to assure boiler flow and that the DHW has a dedicated circ tee'd off the other way. I imagine that both sides have check valves (in the circs?) so that they are not reverse flowing each other?
    A picture from farther back would help.
    If my assumptions are correct, The boiler should be managing all the circulators. This will allow you to run outdoor reset on the heating and DHW with priority.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Sheepman24Sheepman24 Member Posts: 5
    its a primary secondary system with a circulator controlling the boiler loop inside the boiler housing. i can get a better picture later. there is a check valve on the DHW system but there was no call for one on the radiant heat in system piping diagrams in the install manual. i do not believe the pumps have check valves.

    If the boiler is handling the circulator then does that mean that the taco is simply handling the zone valves. most installs I've seen with the taco controllers have the pump controlled by the controller.

    so will i just not use the 120v out on the taco? is that common?
  • Sheepman24Sheepman24 Member Posts: 5
  • ZmanZman Member Posts: 4,855
    The boiler has built in primary/secondary with a check valve and you have a check on the dhw, so you are all set.
    The boiler will alternate the onboard circ and the DHW circ to give you give you the DHW priority.

    I don't think that there is a right or wrong answer for the heating zone circ. If it were mine, I think I would let the Taco control it. That way when the boiler is in DHW mode, the heating zone circ will be moving warm water around, and even out the infloor temps
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Sheepman24Sheepman24 Member Posts: 5
    Thanks for that! i guess the distinction would be is that the circulator would be able to run during DHW priority if the taco ran the show. if it did run then it would be pulling water from the primary loop during dhw priority which has a different heating design and temperature. floor is 120* supply and DHW is 180.

    so then it seems i would want to have the boiler manage this so i am not having both running at once sending water that is too hot to the floor.

    unless im missing something.

    i will run a new 120v supply for that taco that is dedicated.

    Do these taco controllers send signal to the boiler when the call is made or when the valves get open. apparently these actuators take like 30 seconds to open and i think i read somewhere that it waits until they open to call for heat

    only thing left to figure out is how to seal off a few copper unions that have slow leaks... tried plumbers grease to torque them but still have a few that leak even though alignment is good.
  • ZmanZman Member Posts: 4,855
    As long as the boiler circ turns off, no heat will go to the zones.
    The Taco closes the enable switch once the valves are actually open.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
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