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Taco ZVC 404 priority stays lit even when not needed.

actonman Member Posts: 1
The priority zone says it's calling for heat, even though it satisfied. This is preventing my heat zone (1 & 2) from calling for heat. If I turn off the water heater (priority zone) then heat is called for and works. What can make it do this on the priority zone?


  • Alan (California Radiant) Forbes
    Do you have zone valves to your heating and DHW zones? It could be a stuck end switch on your DHW zone valve. Happens a lot with Honeywell V8043 zone valves.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Ironman
    Ironman Member Posts: 7,379
    edited November 2018
    'Water heater". How about some details and maybe some pics? What type of zone valves?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • SuperTech
    SuperTech Member Posts: 2,184
    edited November 2018
    Do you actually need DHW priority? My boiler can handle all my DHW usage without using a priority zone, with a single circulator, 41 gallon tank.
  • delta T
    delta T Member Posts: 884
    You can turn priority off using the switch inside the taco zvc404. That will let everything run until you can get it fixed, but I am betting a stuck end switch on your zone valve as @Alan (California Radiant) Forbes said.