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No Flow Through One Radiant Loop

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MasterC
MasterC Member Posts: 46
edited November 15 in Radiant Heating

I am unable to get any flow through the top zone (Zone 6) in my system. Also, that zone has recently developed a pin-hole leak in the bottom of the copper line just before the first tee to the different sub-loops (see close-up picture), and I wonder if that's related? Any ideas?

I have tried hooking a drain hose to the red-handled hose bib at the bottom and flushing water through, both via the auto-fill valve and by hooking a supply hose up to the blue-handled bib at the top left. While doing this, I isolated all other zones by closing the ball valves by the circulators and also closed the green-handled valve in the return line.

Doing the same procedure to flush any other zone results in flow out the drain hose, but no flow for zone 6. I assume it is unlikely for all three of the loops in that zone to be blocked, so likely the blockage is in the copper piping that they have in common before teeing off? Also, we tried changing out the circulator in case it was seized or something, but it made no difference.

Edit: Note for now I have temporarily "fixed" the pinhole leak with some silicone wrap.

image.png image.png image.png

Comments

  • Ironman
    Ironman Member Posts: 7,807

    What’s the cold static fill pressure on the boiler? What’s the height differential between the boiler and the highest point in the system?

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    bjohnhy
  • bjohnhy
    bjohnhy Member Posts: 111
    edited November 17

    Its not because the valve on return side is closed? See photo. That may be another supply pipe?

    image2.PNG

    If not, I would start by closing the isolation valves for that circulator and removing the circ (vs just loosening one of the flanges enough to visualize any leakge). Then, momentarily open the isolation valve on the supply side, just a smidgen, make sure you are getting flow. Do the same from the heat loops to see if you are getting backflow (i dont see any check valves present). This will help locate a blockage.

    Can you hear the circulator come on when that zone is calling?

    Can you post picture of the return loops?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 11,453

    Looking at the near boiler piping from your boiler photo, it is difficult to determine the direction of flow. I can see the pipe that all the circulators are manifolded to. I can not see where that pipe goes. I can see the supply pipe that connects to the air separator and expansion tank.

    If all the circulators are on the return side of the boiler and pumping into the boiler with the expansion tank on the supply side of the boiler then when the top floor circulator pump operates, there is a possibility that the static pressure minus the pump head (pump's differential pressure ) can create a low pressure condition inside that loop that can actually be lower than the atmospheric pressure. Depending on the location of that pinhole, you may actually get air entering thru that opening, causing a problem with that zone.

    To determine if that is the problem can you answer @Ironman's questions: "What’s the cold static fill pressure on the boiler? What’s the height differential between the boiler and the highest point in the system?

    The "cold static fill pressure" is the pressure on the boiler gauge when no circulators are operating and the boiler is cold (like 3 hours after turning off the switch). The hight between the boiler gauge and the top pipe in the system on the top floor is important to determine what the "cold static fill pressure" should be.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • hot_rod
    hot_rod Member Posts: 26,254
    edited November 18

    A pic showing the relationship, pressure and elevation, psi pounds per square inch

    so a 10' column of water would show 4.33 psi

    Or 4.33 psi would lift water 10' in the piping.

    Screenshot 2025-11-17 at 8.11.56 AM.png

    So for a two story home, boiler in basement 10 psi is adequate.

    Most fill valves are preset at 12 psi, same for expansion tank pre-charge. But always confirm :)

    Some fill valves include a pressure gauge so you are not assuming or believing the boiler gauge.

    \

    Screenshot 2025-11-17 at 8.15.38 AM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • MasterC
    MasterC Member Posts: 46
    https://forum.heatinghelp.com/discussion/comment/1872648#Comment_1872648

    For most of my time in this house, it was around 12psi, which was the setpoint of the fill valve. Recently someone came out to service the system and replaced that fill valve and set the new one to 18psi, which is the lowest pressure I have seen since. It is about 19 feet from the boiler room floor (in the basement) to the 2nd story floor (under floor heating loops).

  • MasterC
    MasterC Member Posts: 46
    https://forum.heatinghelp.com/discussion/comment/1872656#Comment_1872656

    No - that picture was from another time when we were trying some stuff, but generally those valves are open, and that's also not in the problem zone (which is the top circulator in the picture).

    There is a check valve in the return, just to the left of the green-handled valve.

  • MasterC
    MasterC Member Posts: 46
    https://forum.heatinghelp.com/discussion/comment/1872681#Comment_1872681

    Thanks - flow is from the boiler, up to the circulators, which pump from there into the heating loops.

    The pin-hole is approximately where the red circle is in the picture below. This zone has been a problem for years, but I do not think there has always been a pinhole leak there - just noticed it recently.

    image.png
  • MasterC
    MasterC Member Posts: 46
    https://forum.heatinghelp.com/discussion/comment/1872684#Comment_1872684

    Previously it was set to 12psi, but recently it was set to 18psi. And about a year ago the pressure gauge on the boiler stopped working reliably, so since then I crack open this valve when I want to take a reading on this gauge:

    image.png

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