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water hammer???

vinceM Member Posts: 81
Hello all.
We've been having an issue with what I believe is a water hammer problem. However, it doesn't appear to be the typical hammer. In the past I've heard the hammer a short time before or after the cycle (Which I would like to correct)what's currently occurring is the hammer seems to strike with no real "connection" to or independent of the heating cycle. There most severe hammer seems to come from the riser to the second floor bathroom radiator. It does occur at one of the main floor radiators also but much less intense.
We have a one pipe steam system. The home was built in 1929, there is no insulation in the walls. ALL the exposed pipes are insulated and all the lines are properly pitched and all mains(3) are adequately vented.
Any thoughts?


  • MartinBarry
    MartinBarry Member Posts: 2
    Do you know if the pipe in the wall is still insulated ?
    Is this a young boiler ?
  • Fred
    Fred Member Posts: 8,542
    It sounds more like Expansion/Contraction noise. Water hammer will occur when steam hits a pocket of water, during a heating cycle. Noises before or after a cycle is typical of expansion or contraction. If that riser is rubbing against a floor board or joist it will make that noise before or after a heating cycle. see if you can find a location where it might rub or where a fitting might get hung up on a some part of the house structure. If it is rubbing, you can cut a strip of plastic milk carton and wedge it between the pipe and the structure to allow the pipe to slide. If a fitting is hanging on a floor board, notch that board a little to allow clearance.
  • vinceM
    vinceM Member Posts: 81
    The boiler is 30-40 years old.
    As the house is 80+ years old there wouldn’t be any insulation in the interior walls. No records show any renovations that would have placed insulation. We’ve been in the house for 10 years.

    Fred, I’m relatively confident of the location of the suspect pipe but I can’t get to it without opening a plaster and lathe wall. Here’s where I struggle with the issue: I clearly understand the physics behind the expansion/contraction and how the pipe comes into contact with an adjacent structure, be it a joist or stud, etc. What I don’t understand is how the actual sound that’s heard is created. To me, a pipe that’s moving(rubbing) against a wood structure wouldn’t make that particular sound.
    It sounds to me like the pipe is being “slammed” against a structure not “rubbing” along it.
    Can you clarify....
  • Fred
    Fred Member Posts: 8,542
    Can you record and post the sound so we can hear it? Is there any possibility the radiator that pipe is connected to gets hung up on the floor, when it expands and/or contracts and then pops loose and that rapid movement causes the hidden pipe to bang against a stud? Try putting some slips of plastic under each foot of the radiator and see if the bang disappears.
  • neilc
    neilc Member Posts: 2,664
    try "slipping" the pipe to the floor also
    known to beat dead horses
    JUGHNE Member Posts: 11,021
    I have some 100 YO single pipe rads in a church that will ping/ding as the rad itself heats up.
    These are old column units that are not connected across the top, (1 Pipe steam only), I believe the top of each section flexes as it heats and may ding to its neighbor. Iron to iron noise.
  • vinceM
    vinceM Member Posts: 81
    Thanks for the responses.
    Fred, I thought of recording the sound, however, it happens so fast, it’s only one loud “CLANG” (like a metal hammer striking a hollow metal pipe)when it happens and I’m never ready for it. Your idea about the riser to the radiator getting “hung up” is a possibility but the strange thing is that the sound occurs very randomly. In fact I’ve noticed that it happens well before or after a heating cycle when the rad is cool.

    I have to say, I really can’t tell if it’s the actual rad that’s making the sound or if it’s traveling up from a somewhere in the run.

    JUGHNE brings up an interesting thought.
    However, all my rads have sections that are connected across the top and bottom.

    There is one rad, on the main floor, directly above the boiler in the basement that seems to be the one most affected.
    Aside from it being the 2nd largest(section wise, 14) there’s nothing particularly unique about it.

    I’ll try the plastic under the feet technique and get back to you.

    Thank you again.
  • Fred
    Fred Member Posts: 8,542
    @vinceM said: but the strange thing is that the sound occurs very randomly. In fact I’ve noticed that it happens well before or after a heating cycle when the rad is cool.

    It definitely is expansion/contraction noise. Actual water hammer occurs when steam hits a pocket of water, during a heating cycle. It may be a pipe or it may be a radiator but it isn't "hammer" Try the plastic under the feet of the radiator that is noisy.
  • Shalom
    Shalom Member Posts: 165
    You could also jam some plastic around the pipe into the hole in the floor; it may be rubbing on the wood of the floor. I have one such radiator that clanks once on heating and again on cooling, and sometimes it won't clank until someone walks on the floor nearby and causes it to flex.