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Control to give HW priority to indirect HW heater

Steve Garson_2Steve Garson_2 Member Posts: 636
I have a WM GV-5 boiler with 5 zone valves: 4 for radiators and 1 for the indirect HW heater. The Amtrol Boilermater 41 gallon HW heater does not provide enough water to fill a bath tub half-way. I believe this might be because the HW heater does not have a way to prioritize the boiler and shut down the heating zones to heat the water.

Can someone recommend the type of control that I need to get the right hot water output? Or should I have a separate circulator for the HW heater? Or both?
Steve from Newton, MA


  • Jamie HallJamie Hall Member Posts: 14,945
    What zone control are you using? Some have a built in switch for domestic hot water priority, which you need.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • hot_rodhot_rod Member Posts: 14,425
    How old is the tank? Those finned copper coils inside tend to lime up over time and performance drops.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    ZmanSteve Garson_2
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 8,123
    Taco zvc406-4 is what you need
  • ZmanZman Member Posts: 6,340
    hot_rod said:

    How old is the tank? Those finned copper coils inside tend to lime up over time and performance drops.

    They don't transfer much when new, the lime plugs them up quickly.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Steve Garson_2
  • EdTheHeaterManEdTheHeaterMan Member Posts: 1,636
    edited January 13
    What size piping is on the boiler side of the system. I have seen them piped from the boiler to the indirect with 3/4" copper. This is no better than a 40-gallon gas water heater with a 40,000 BTU burner. You need to pipe the boiler side with 1" minimum. Then use 1"copper x 3/4" pipe adaptors at the tank connections to get the full rated capacity.

    The next thing to look at is the zone valve. Are you using the old Taco 570 zone valves? They take forever to open. You may be 1/2 way thru the hot water in the tank before they even turn on the boiler. Then there is the boiler pre-purge cycle before the flame starts to heat the boiler water By the time you start to get 180° boiler water to the tank's heat exchanger... you are nearly out of hot water. Then you are playing catch up. Change to a fast acting zone valve

    Next thing is to get the priority control like the ZVC 406 mentioned by @EBEBRATT-Ed.

    Finally, if that is not enough, you can set the tank temperature higher like 140° or 150° and install a mixing valve on the hot outlet of the tank.

    Respectfully Submitted
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
    Specialized in Oil Heat and Hydronics where the competition did Gas Warm Air

    If you make an expensive repair and the same problem happens, What will you check next?
    Steve Garson_2
  • Steve Garson_2Steve Garson_2 Member Posts: 636
    Thanks everyone for the tips. Installing the Taco 5-zone control with priority for the HW heater solved the problem. Since all the wires needed extending, it took almost three hours, but now we fill the bathtub without any problem. Happy wife! Thanks!
    Steve from Newton, MA
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