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Sanity check on replacing flow check valves

I have a 3 zone system and want to replace all the flow check valves since I'm having issues when the 2nd floor is calling for heat, the hot water also flows into 1st floor even though its not calling heat so on and so forth. I haven't done this before but I have a plan written and would love your thoughts:

My setup:

Flow check valves:

1. Switch off power to the boiler
2. Turn off gas to the boiler
3. Close off water supply going to boiler
4. I'm assuming I need to drain the entire boiler to change the flow check valves. Can I simply just drain everything from that one valve on the bottom of those pumps or would I need to drain each individual zone according to the picture?:

5. Replace all flow check valves
6. Turn water supply back on
7. Re-light gas pilot
8. Bleed the system
9. Turn power back on boiler


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,257
    edited February 2020
    Gonna have to drain it all. I'd recommend weighted flo checks.
    While everything is drained, move that expansion tank and properly mount it to the wall with a bracket, and add a Webstone expansion tank valve for easier isolation, checking charge and eventual tank replacement. At least check the charge while the system is drained. Should be the same pressure as you'll want for the entire system when done purging.
    It's an easy purge by closing each valve above the circulator, attaching a hose to the drain above, and purging one zone at a time, keeping the pressure up around 20 psi the entire time.
    After you purge a zone, open the valve to purge thru the boiler, then close that valve and repeat for the other zones.
    Then when completely finished bleed off some water to get the pressure down to where you want it.
    All purging done with boiler off/circulators off.
    I don't see signs of any good air separator/removal, so you still may have some air problems, unless the heat emitters are radiators and you have option to bleed upstairs.
    Cycle each circulator for a couple of minutes, then repeat the entire process if necessary.
    You're also pumping into the expansion tank, which doesn't help.
  • Intplm.
    Intplm. Member Posts: 1,470
    Maybe change them those sweat checks, (all of them to threaded type .) Unscrew and cut away what you have right to the tees and go from there.
    And what @STEVEusaPA said.
    EBEBRATT-Ed Member Posts: 13,813

    Your sequence of work is correct.
  • darklunar123
    darklunar123 Member Posts: 5
    Thanks for the tips guys.

    So just to be sure for step 4 on draining all of the water from the boiler, I should be doing, please correct me if I'm wrong:
    1. Close all 3 valves above the circulator
    2. Attach a hose to one zone
    3. Open spigot until no more water comes out of hose
    4. When no more water comes out of hose, open valve for that zone with the hose attached
    5. I'm assuming when no more water comes out of hose, close spigot
    6. Close valve with the attached hose
    7. Repeat steps on the other zones

    Do I have to do anything with that spigot that is at the very bottom of the circulator?

    After I have replaced the flow check valves and turn the city water back on, should all 3 valves be open or it doesn't matter?
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 3,723
    edited February 2020
    You can drain all the zones at once from the hose bibb below the first pump. Steve was detailing the procedure when you refill the system.
    After you drain all the returns, you will still have water in the supply pipes. That old Hydrotherm should have a drain, but those check valves, if still operating properly will be holding back some water. When you cut into the pipes after the check valves, have a small, plastic bucket at the ready with a 5 gallon bucket on the floor next to you so you can empty the small bucket when it fills up. Lots of rags and cover the electronics at the boiler so they don't get wet. Best when two people are involved.
    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: 19,924
    I prefer the spring type hydronic checks. They are very flow friendly and are 100% "bubble free" closure. Basically the same check found in circulator.

    This version is also serviceable should some crud get stuck inside.

    Looks like all those old flow checks have or are leaking.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Love the Caleffi checks, their serviceability and high Cv. Expensive, but quality and performance aren't cheap.
    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