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Adding pressure to a system with zone valves

joeba Member Posts: 24
On a system with zone valves on the supply, and the circulator on the return(007 no internal check), do you have to open zone valves? I am assuming no, since the auto-feed has no idea if the zone valves are open or closed


  • Jamie Hall
    Jamie Hall Member Posts: 23,536
    No, you don't.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • joeba
    joeba Member Posts: 24
    So I always like to know why. What happens if you do open them? Does it matter?
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,075
    edited September 2022
    If you add water with the zone valves closed, water will be added through the pump on the return as there is no check valve. 
    If say, there is a flow check on the pump, the location of the fill valve in the system will determine the outcome. 
    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
  • hot_rod
    hot_rod Member Posts: 22,341
    The additional water (pressure) will go somewhere- into the boiler, expansion tank, piping, etc.

    Check the expansion tank pre-charge pressure before you add water and occasionally through the years. You need to isolate or remove the tank to do that.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream