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Weil McClain Ultra 155 DHW Priority Issues

bzevotek Member Posts: 2
Hey, guys here's the setup I currently have running.

I have three zones, one for the bedrooms, one for the main floor and one for my basement slab. These are on two Taco boards since the bedroom zone is separated with actuators for each room and has its own slaved taco board. The second taco board is connected to the boiler and has the slave, the slab and the main floor zones. I HAD an indirect on DHW loop and set to priority 1. I replaced it with an electric on-demand and disconnected the zone 1 pump and wiring from the boiler.

First Question: Did I need to replace the DHW? Can I draw domestic directly from the boiler using a flow switch (if that's even needed)? (I'd be running an open-loop and need to flush the system and probably put in a filter or use softener water.)

Second Question: Can I move the bedroom zone pump and Taco board wiring to Zone 1 and set it to boiler priority 1? I am having issues separating which zones and pumps are needed on the boiler set up. I want the bedrooms to be priority 1 since we have a baby. Then I assume I could set each of my remaining zones to pump 2 and 3 on the boiler control.


  • Dave H_2
    Dave H_2 Member Posts: 560
    Second Question:
    Priority is systematically used for DHW. What that means is when there is a call for heat from the boiler from the priority zone, turn on that zone and turn off all others.
    The reason for that is so that the boiler size does not need to be upsized for the DHW zone and the heating zones combined. The run time for the DHW is typically short and having the heating zones off for that amount of time is not noticed.

    I wouldn't change a thing in the wiring.

    First Question:
    NO, this is a closed loop system. Your former indirect had a heat exchanger that transferred the heat from the boiler water to your potable water.
    A closed loop system means the water that is in there is permanent and does not come out (only on purpose when servicing if needed)

    Dave H.
    Dave H