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How to control a primary pump

How to control a primary pump for a primary-secondary hydronic system.In the book " Pumping Away", Mr. Holohan writes about how to set up everything, but I can't find how best to turn the primary pump off and on in reference to any of the secondary pumps.


  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I do not know about most boilers and their controls...

    ... but on the W-M Ultra-3 boilers it is pretty easy. Its uControl board has three inputs from thermostats (you need not use them all) and three outputs to drive circulators. Each thermostat has its own reset curve for outdoor reset.

    The control board allows you to select which circulators run with which thermostats. I have two heating zones and one indirect fired water heater zone, zoned with Taco 007-IFC circulators. Let us call the circulator for the water heater #1, the primary circulator #2, and the secondary circulator for downstairs #3. The secondary circulator for upstairs is #4.

     This is set up is that the Priority 1 thermostat is from the domestic indirect fired hot water heater, and you set it up to run just the circulator for that #1.. That is just across the primary loop. For the other two, that are piped primary-secondary, you have it run the primary circulator. (I wish they had 4 outputs.)

    So for my downstairs, I use priority 2 and have it run the primary circulator #2 and the circulator for the downstairs zone #3. For upstairs, I have an extra relay to run the secondary circulator for upstairs #4 and the control board runs just the boiler circulator #2.

    This is all described in the boiler installation manual for the Ultra-3. I would imagine there is something similar for other boilers.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,285
    It is usually end switched

    The circulator can be turned on when any of the zones call for heat. This is done with its own relay if one is not built into the existing or new boiler depending on if it is a repipe or a boiler replacement. I take the end switch from the zone circulators and run it to the primary circulator TT terminals and then run the end switch from that to the boiler TT terminals with consideration to al the saftey controls for the given boiler. There should be diagrams for your boiler in the owners and instalation manual. Your electrician should be able to work out the details.
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