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thermosyphoning

Kevin Seiler
Kevin Seiler Member Posts: 2
in THE MAIN WALL
Date: December 08, 2003 04:54 PM
Author: Kevin Seiler (kseiler@mullenrefrigeration.com)
Subject: thermosyphoning



I have a single story home that just had a three room addition. The crews installed a new 3/4" run to the new addition while the original system had a parallel 1 1/4" run. The new zone has a single 3/4" W/R 1361 zone valve while the original house also has one W/R 1361 to serve the two 1 1/4" runs. The zone valves were put on the return side just before the pump. The zone valves also have isolation valves just before them for service reasons. When we wired up the new 3/4" zone and fired it up we got hot water finding it's way out of one of the 1 1/4" supply lines of the other zone, even with the isolation valve closed on the return line of this 1 1/4" loop. (The isolation valve serves both 1 1/4" supply loops on this original house piping.) The guys say there is no cross piping. The original house is now overheating. Can thermosyphoning be the issue even though it is only a single story house. All areas are served by baseboard, old house is iron while the new is finned tube.








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Comments

  • Steve Eayrs
    Steve Eayrs Member Posts: 424


    Sounds like it could be a couple of problems. Bleed-by on the old zone valves, and/or the need for a check valve somewhere. May take someone to look at it to determine the problem.
    Steve
  • Tony_8
    Tony_8 Member Posts: 608
    White-Rogers

    zone valves are not 100% shut-off. They have quite a bit of bleed-by. You may need to get a more positive shut-off type valve(s).
  • Tony_8
    Tony_8 Member Posts: 608
    how does

    it siphon if it's NOT bleeding by "much" ?

    Keep your responses on The Wall so maybe someone else will see and have a fresh idea.

    Tony
  • hr
    hr Member Posts: 6,106
    You can

    actually get small amounts of ghost flow backwards up a pipe. A two direction flow, of sorts. Maybe a spring check or flow check on the supply would be all that is needed.

    This is more common when the piping is taken off and run up above the boiler. Thermal drops can also help sometimes.
    but a flow check is generally an easier retrofit.


    Ghost flow is a tricky troubleshoot.

    hot rod

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  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    How are the supplies piped?

    The supplies to the original 1 1/4 inch zone must be joined together before they are connected to the piping that also supplies the new 3/4 inch zone. If they are not, ghost flows will occur because of minute pressure differences in the supply piping as the water moves through it. The water will flow out one supply to the old zone and return through the other supply.
    If the piping is not easily joined, two flo control valves can be used on the two supplies to the original zone supplies.
    I see this problem all the time on systems installed from the 1950s to today. I use White Rodgers zones valves quite often and have yet to have problems with the very slight leak by causing control problems.

    Boilerpro
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