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Steam air vent spitting water and hammer/banging noise

I need help from the experts. I am a first time homeowner and this is my first winter in a house that was built in 1925. I am having a few issues with my heating.

1. One radiator ( small one) produces a lot of hissing sounds.

2. One large radiator ( baseboard) air vent valve is spitting water.  Additionally it procudes hammering/banging noises in the morning when the heat comes on. Searched on the internet which said I should try 3 things.

a). Replace the air vent valve.  Replaced with what was in there before. Maid-o-mist #D. The spitting reduced but is still there.

b). Check the slope such that the vent valve is slightly higher than the input side. Checked with a level and it is above it.

c). Make sure that the valve is in the open position.

Is there anything else I can do? Any other vent valve I can use to replace it?

One of the guyz who came to check said that it would cost about $1800(very steep) to fix the above stuff and these problems exist.

  He said that the main vent was installed in the return line and not the line that goes up.

And said that there was a clog in the boiler.

I saw that Home Depot sells clog removers(liquid) which I do not know how to use? How to put it in?

Not sure of the main vent but when I touch it the pipe that does not have the vent is hotter than the pipe with the vent..

About the boiler: Has a low shutoff valve. THe pressure gauge is either broken or stuck at 0. Almost every other day I have to drain the boiler and replenish the water. If I do not do so then within a week the boiler shuts off due to low water.

I am attaching a few pics of main valve, boiler, boiler model, pressue gauge and air vent valve.

Any help will be appreciated.


  • BobC
    BobC Member Posts: 5,470
    Too much water is bad

    Adding more water to a boiler will shorten it's life dramatically because of the oxygen in the added water. When water is added the boiler should be brought up to steam to drive off any dissolved oxygen. Does water seem to return to the boiler after iot's been off for a while?

    The first job is to find out where the water is going, do you have any boiler return lines that go below the cement floor? If you have a blocked return line it has to be taken apart and snaked out or that pipe has to be replaced. there is no chemical that will do this for you.

    One of you pictures shows a main vent that is probably much smaller than you need. If a main vent isn't working or it's to small your wasting fuel and the heat is usually uneven. How long is the steam main and what size pipe (outside circumference is fine - a 2" pipe is about 7.4" around and a 2-1/2" is over 9" around), once we know that we can tell you what kind of main vent you should have.

    Radiator vents should point straight up to work right. There is a pressuretrol on the boiler, what is the tab on the front of it set to and what is the white wheel inside set to? The boiler should be running at 2 PSI or less. Your 0-30 gauge may not be working and even if it does they are not much good at the low end.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Jamie Hall
    Jamie Hall Member Posts: 22,877
    Where to start...

    First things first -- the main vent is probably too small.  It is also not in an ideal location, although it can work there.

    The hissing vent and spitting water suggest rather strongly that the boiler is shutting off at too high a pressure.  I'm honestly not familiar with the pressure controller shown on the boiler, but perhaps some else is -- and whatever it is, it should turn off the boiler at 2 psi or less and back on at about 1 psi.

    Another possibility, though, is that the near boiler piping is a little strange.  Unfortunately, your photos don't show all of the near boiler piping, so I can't be specific -- but it does strike me as a possibility.  This would cause water to mixed in with the steam, which could also cause the spitting and also the hammering and banging (though not the hissing).  More pictures of the boiler would help, showing all of the piping associated with it.

    Do NOT put a "clog remover" in the boiler.  In fact, don't put anything but water in the boiler.  I doubt very much that a "clog" in the boiler would cause any of your symptoms.

    I am concerned about your comment that almost every day you drain the boiler and replenish the water.  How's that again?  It shouldn't be necessary to drain the boiler but once a year!  It's not a bad idea to flush the gunk out of the low water cut off once a week or so, but drain the boiler?  Ah... no.  Just drain enough out of the LWCO to run more or less to clean, and then refill to about half way up the gauge glass.

    Related to that is your comment that if you don't do the drain/refill bit, the boiler shuts off on low water within a week or so.  You shouldn't be losing enough water to get to the LWCO in a season, never mind a week.  You may have a leak somewhere.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • incorrect description

    Incorrect description.

    Thank you for your replies. Sorry about the incorrect description of draining the boiler.  When I said I drain the boiler what I meant was that I open it up to remove the water that is dirty and when it is clear fill it with the water halfway to gauge glass . When I bought the house the previous owner ( who happened to be a contractor and owned the house for 10 years ) told me that I need to do this about once a week to maintain the boiler.

     The air vent that is spitting water does leak an appreciable amount of water ( about 10 ml or so in a day). That vent is in a radiator that is in on the second floor of the house in the bedroom farthest from the boiler.  The vent is actually pointing upward ( the photo is taken sideways).

     I am totally clueless about how to check if the return water is coming in after the boiler has stopped running. I see the gauge glass and see that the level comes down everyday by a bit. I will check the size of the pipes and post it.

    Where is the pressuretrol on the boiler supposed to be? I cannot see it or I am missing the obvious?

    I will post more pictures of the boiler piping.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Spitting vents

    Definitely lower the pressure (you may need a modern pressuretrol/vaporstat), and verify it with a good low-pressure gauge (gauge store.com, 0-3 psi) post a close up picture of the pressuretrol, so someone may recognize it and know how to set it. It looks to be above the LWCO.

    Insulate your supply pipes with fiberglass, so you won't have so much condensation before the steam gets to the radiators.

    Replace the main vents, with gorton 2's, if there is headroom. The air should be able to escape at 2 ounces.

    If you have any radiator vents which are bigger than a Hoffman 1a, then reserve them for locations with a long riser.--NBC
  • SWEI
    SWEI Member Posts: 7,356
    remove the water that is dirty

    approximately how much water are you removing every week? 
  • Re: dirty water

    I remove about 2-3 litres of dirty water in a week. Have to do it almost every day and so in the week it would be approximately that.
  • main vent and pipe sizes

    The main pipe is 1.9 diameter.

    The return pipe is 1.315 diameter. The main vent is attached to this line. It has USAV 883 on it . Attaching picture.

    The pressuretol shows 1 ( attaching picture).

    The lines near the boiler do have the insulation.
  • boiler pictures.

    Thank you for the replies. I am also attaching the pictures of the piping around the boiler.
  • water return to boiler

    How do I check if the water has returned to the boiler after it has been off for a while? The return lines are all on the cement floor except right by the boiler where they go in partially for a bit.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    dirty water

    steam boiler water is usually the color of weak tea, so don't worry about draining it so much, and certainly do not add any magic potions to the water, even if endorsed by famous hockey players, and politicians!

    i think we have said all we can about low pressure, and good main venting, coupled with slow radiator venting.

    i am sure, by now that all the loose sediment in the bottom of the boiler will have washed out. just keep the level up to the line, and look for any leaks.--nbc
  • How to reduce the pressure + replace main vent

    Attached a picture of what I think might be the pressuretol. It shows a reading of  1. How do I adjust it down?  Any precautions I should take.

     I looked at other posts and it says that there they should be a low pressure start and another end.  This does not show it.  I might not be looking at the right tool though.
  • icesailor
    icesailor Member Posts: 7,265
    Hydronic hot water boiler:

    That looks like an effective start/supply for a hot water boiler.

    The same for steam?
  • BobC
    BobC Member Posts: 5,470
    Bouncing water?

    The pressuretrol on your boiler is unusual, if it's set to 1 that is probably as low as it will go. Does the water in the sight glass bounce around a lot when you are making steam? You could have some oil in the boiler water and that would cause problems that can be solved by skimming the boiler. Replacing the boiler water won't help if skimming is needed because the contaminants just cling to the inside of the boiler and mix with the new water.

    If you have clogged return lines or a lot of sediment in the boiler that has to be fixed for the boiler to work right.

    You mentioned you had replaced a maid o mist D vent on one of your radiators. That is an aggressive vent that may be adding to your symptoms. Make a list of the radiators in the house listing the height, width, and depth of each one. include the number of columns and how many sections wide each is and what kind of vent is on each radiator.

    That usav main vent is probably too small you might want to try a maid O mist #1 main vent in place of the USAV and you may need more than one depending on how long your main is. You want to vent the mains fast and the radiators slowly for good operation.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Re: bouncing water

    Thank you for your replies.

    The water in the looking gauge does bounce when the boiler is making steam. Is that a bad thing?

    Describing the radiators in the house.

    First Floor:

    1 Baseboard

    55 inches length of the pipe.

    5 and a 1/2 inches circumference.

    The valve is a Maid o Mist Jacobus #C

    2. Baseboard

    60 inches length

    Jacobus #A

    3. Radiator

    15 inches length

    4 inches depth

    25 inches height.

    Valve is Jacobus #C. This raidator hisses a lot and just noticed today that is also leaks water.

    2nd floor:

    4. Baseboard:

      96 inches long.

      Valve is  Jacobus #D.

    Has a couple of tiny brass elbows that let the valve be higher than the pipe and also face upwards.


    5. Baseboard:

       50 inches length.

       Valve: Gorton ( I think C). Difficult to read this.

    6. Baseboard:

       96 inches length.

       Valve is #D. This radiator is the one whose valve is leaking.

    For the 6) The banging noise has gone away. Couple of things I did was

    a). Change the direction of the valve to be exactly straight up. I had to move a couple of brass elbows.

    b). Due to the added room, I could raise it the radiator a bit more.

    The water is still coming up at the beginning when the heat starts up. About 3 ml or so every time and then it stops. Any other ideas on how to stop this leak?

    Was trying to replicate the brass fittings as being above the pipe for 6) ( the way it is in 4 : will attach a pic of 4) ) I am unable to change the direction of the valve as when they put it in , they put pipe joint compound instead of teflon.

    Any ideas on how to unscrew it? Tried tightening to unscrew or cutting a slice but nothing gives. Still need to try heating but with a candle instead of propane torch ( My wife will not allow that). Anything else I could try.?


  • David Nadle
    David Nadle Member Posts: 624

    It's not just a good idea to drain some water, maybe a quart, through the low water cut off once a week. It's very important that you do that to keep the float moving freely. However, you don't have to drain water every time you add water. You can just add fresh water very slowly until the waterline is in the center of the glass.

    I think it's possible that all the lost water is from steam leaking out of your vents. In my opinion the vents are the first thing you have to address. All of your radiator vents are very fast, and your main vent is probably too slow. This is the opposite of what you want. The one with brass fittings is angled so that condensate will pool up inside it and get blown out every cycle.

    You could cut most of that off with a mini hacksaw then unscrew the remaining elbow with pliers. I think it should be replaced by a single 1/8" street elbow -- black iron, not brass air fittings! Then find a straight vent, not a 90 degree vent, and not size C or D, size 5 or 6.

    I think you should try replacing all your radiator vents with slower ones, 5 or 6, and get a fast vent like a Gorton #2 for the main vent. Make sure all your vents are installed vertical and clearly drain back to the radiator.
  • JStar
    JStar Member Posts: 2,752
    edited January 2013

    That vent looks like it slopes the wrong way. It'll collect water and never drain out of the brass fittings.
  • BobC
    BobC Member Posts: 5,470
    It's all in the venting

    I agree with what JSTAR said in his post about the vents you are using and that one with the bad tilt - that guarantees spitting.

    When you use aggressive radiator vents you create a lot of condensate and that encourages a problem like your seeing on your system.

    Install high capacity Main vents and try slowing the radiator vents down to 4's or 5's; I think that may go a long way towards solving your problem.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Replacing vents

    Thank you guyz. WIll order Gorton #2 main vents and slow down the other vents. Was down with flu and could not work on this for a while.


     I see that the Gorton #2 are 1/2 inch . But it seems that my main vent is 3/4 inch. Is there a way for me to  get them to be compatible ( any connector I can use in between? )
  • Rod
    Rod Posts: 2,067
    edited January 2013
    Adapter for Vent

    Use a 3/4 MPT X 1/2 FPT bushing. They are available at any plumbing store or Home Depot plumbing section.

    - Rod
  • replaced vents

    Replaced the main vent with a Gorton #2 with the bushing and the radiator vent. I do not see any difference as yet.

    The problem radiator is still spitting about 3-4 drops of water per cycle. I cannot see the pitch of the pipe that is going to this radiator ( under the floor).

    The banging noises are still present and I can hear them from multiple radiators when the heating starts up and sometimes when it goes off. Could that be due to expansion or cooling? Is that dangerous or just annoying?

    Are there any other things I could try to fix these issues?
This discussion has been closed.