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which come first backflow preventer or pressure regulator valve to the boiler

mercedes Member Posts: 65

My neighbor house has hot water system with cast iron convector radiators. The last radiator on the line was making gurgling sounds. We bled the radiator and air came out but no water. Went to the boiler room raise the handle on the PRV and water went in. The noise is gone now and when bleeding water comes out. But I notice the backflow preventer and PRV was replaced several years ago (still looking new). The order confuse me. The water flow to the boiler from the street is that the PRV first and then the BFV then to the boiler. I think this is backward? or is it because the system has a steel compression tank in the ceiling in the boiler room. Would the PRV try to fill the steel compression tank and that the reason why the PRV is first and follow by the BFV? if so Next question how would the system ever get make up water or it has to be part of the yearly maintenance?
Thank you again


  • kcopp
    kcopp Member Posts: 4,386
    You are correct... it is backwards. PRV (1156F watts) needs to be on the boiler side of the BFP (watts 9D)
    There are other makes like Taco and Caleffi that I am not sure of the numbers.
  • PhilDavid
    PhilDavid Member Posts: 68
    I’ve seen my fair share of boilers with the back flow preventer after the auto fill/PRV with no issues. Is this correct? Don’t know. But I will say that all backflow preventer autofill/prv’s I’ve installed have then back flow first. And if not a combo they are installed the same as combos.
  • PhilDavid
    PhilDavid Member Posts: 68
    On second thought... backflow preventers have a sediment screen on the inlet. I would imagine this protects the back flow and PRV. I’ve found those screens clogged so check that before condemning the PRV
  • Zman
    Zman Member Posts: 7,542
    The BFP needs to go first. Otherwise the PRV cannot "see" the true pressure of the system. It is a fairly common mistake, but a mistake none the less.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • mercedes
    mercedes Member Posts: 65
    THANK you all for your time. Will flip the BFV and PRV. Will measure the static pressure after ward.