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Steam boiler banging, hissing and water noise

albertbalbertb Posts: 18Member
I have a Weil-Mclain P-468-S Boiler in my house. It's a two family home and this unit is heating just the second floor which is roughly 1300 square feet.

Lately I've had extremely loud banging noises (especially in the morning) in particular from the radiator in the bedroom but it can be heard from other radiators as well. It's loud enough to wake me up every morning. Additionally the bedroom radiator sounds like there is water bubbling inside of it. There is also short hissing from almost all the radiators.

I've been reading a lot of posts and I'm part way through the book We Got Steam Heat. I have insulated the steam main pipe going across the basement (not reflected in these pictures) but that hasn't made a difference. I'm running under 2 PSI but with a 0-30 gauge I can't see what actual pressure I'm on.

A few months ago my steam release valve (pictured) started leaking then it stopped on it's own. Could that be the problem? I haven't had any other movement of pipes or changes in the system that I can think of.

Here are some pictures. I have a Vent Rite 75 main air valve right now.

My steam main pipe is 21.5 feet long and I think it's 2". The dry return is about 20' long and 1". The pipe to the Vent rite is 1" or 3/4", I'm having a tough time getting an exact circumference measurement to match up to the conversion chart on this site.

I hope I provided enough information to come up with some steps for me to correct my issue.


  • icesailoricesailor Posts: 7,265Member
    Banging Heads of Steam Pro's:

    See the below PDF of the installation instructions for your P-68 Weil-Mclain. Read and look at page 11. If you decide that your boiler isn't pipes like the one in the manual, you probably need to call a Steam Professional to attend to it. If that "Pro", like the one who installed it 20+ years ago doesn't recognize the problem, find a REAL Pro that does.

    Its amazing what one can learn by reading installation manuals.
  • BobCBobC Posts: 4,983Member
    Get a level

    The boiler piping isn't correct but that has not changed so lets concentrate on what might have changed. Steam hammer is caused when steam comes across sitting water, that causes the steam to collapse and that is the bang you hear.

    Put a level on all the radiators and make sure there is a little pitch so water can drain back out of the radiators.You can use quarters to raise the radiator feet up a little if you have to, if you need more lift cut some strips of plywood and use that if you need 3/8" or more. Next use the level on all the horizontal pipes in the basement and make sure they all have pitch so water can find it's way back to the boiler, houses settle and something may not be pitched right.

    A Ventrite 75 is pretty low capacity, how long are the steam mains and about what sized pipe? It's best to vent the mains very fast and the radiators slowly, you probably need a faster main vent. What kind or air vents are on the radiators?

    That relief valve should be replaced because a leaking valve can slowly build up crud that prevents it's operation if there was a pressure problem, Also the pigtail under the pressuretrol should be checked to be sure it's not blocked (this should be done every year). The 0-30 PSI gauge is pretty useless down at the 1-2 pound rage where your boiler should be running, think about adding an auxilliary 0-3 PSI gauge so you can see exactly what pressure the boiler is running at.

    The sight glass is leaking at the bottom of the gauge, get some rubber gauge glass washers and then clean or replace that gauge glass. I would also flush out the boiler to get rid of all the rusty water. This should be done when the boiler is cold or just warm with the power off. After the flush while your filling the boiler back up, turn the power back on and make sure the boiler does not start till the water level actuates the float in the low water cutoff. That low water cutoff should be disassembled and cleaned every year or two. After all this run the boiler up to steam to drive off any oxygen in the fresh boiler water.

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

    The near boiler piping is pretty bad. You don't have an effective header. This can lead to water being carried into the system which will then result in water hammer.

    That being said, you need to figure out what changed. Why was there no hammer until now and why are you currently having water hammer?

    The first thing that I would check would be the water quality. Steam boilers will all gradually accumulate sludge in the the boiler. That can lead to surging which in turn will shoot water out into the system. With the current piping, you already have two strikes against you. Try flushing out the boiler a few times and see what happens.

    Check your main vents. If your main vents used to work properly but now dont open properly then the steam be slower then it was previously. The result will be more condensate and more water hammer.

    Check the pressuretrol pigtail. If the pigtail is clogged then the pressuretrol will be useless. The result will be high pressure,slow condensate return,water in the mains and water hammer.

    Setbacks. Did you recently set your thermostat for night setbacks? Setbacks can result in water hammer due to the long run times and colder pipes. Result again will be too much water and water hammer.

    Clogged returns. It is possible that the returns have clogged. Result will be water building up in the main and water hammer.
  • Jamie HallJamie Hall Posts: 10,866Member
    That steam release valve

    is a safety valve.  It is set at 15 psi.  There are two possibilities as to why it started leaking: either it has failed -- which is unlikely -- or the boiler managed to get to 15 psi.  Either way, that valve must be replaced.

    Part two: there is the possibility that the boiler managed to get to 15 psi.  That means that either the pigtail to the pressuretrol is blocked or partially blocked, or the pressuretrol has been bypassed or failed.  This must be investigated and fixed if fixing is needed.

    Both of these items are urgent; having them attended to yesterday morning is none too soon.  There are safety implications here...

    OK.  We got that far.

    The boiler piping is incorrect, and you are getting wet steam -- almost without a doubt.  It is possible that this is not causing a problem, but I wouldn't bet on it; it depends very much on whether there is a drip on that steam main before it heads upstairs.

    The particular radiator which is banging... water hammer.  Several possibilities.  Trace out the piping, and make sure that every foot of any near-horizontal pipe is pitched to drain, either back to the boiler or to a drip.  No sags, no dips.  Make sure that the radiator is pitched back to the inlet (I'm assuming here that we are talking one pipe steam!).  Make sure that the valve on the inlet is fully open.

    That will do for starters, anyway...

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • albertbalbertb Posts: 18Member
    pg 11 of manual

    icesailor Thank you. I'll read this manual and compare it to my system tonight then find a pro who agrees that the piping is incorrect.
  • albertbalbertb Posts: 18Member
    re: Get a level

    Bobc - regarding the suggestions, here is what I have and haven't done.

    I have all the radiators slanted to drain back out.

    The steam mains are 21 feet long and I believe it's a 2" pipe. The air vents on the radiators are the home depot ones that have a round scale of 1-10 adjustment on them. Here is the title on the home depot page: 1/8 in. IPS Angled Adjustable Steam Radiator Valve

    The pigtail was just installed when a full cleaning was done this winter.

    I'll fix the sight glass washers and replace the glass. Thank you.

    I flushed out the boiler just last week but there was no change in the noise or bubbling. The power only comes on once the water reaches a minimum level in the glass. Also I do have the system cleaned every other year.

    Thank you again, this gives me a few things to check and report back on. Your help is appreciated.
  • albertbalbertb Posts: 18Member

    Hi BN -

    I'll have a professional look at the piping and header.

    I emtied the water (just once) but I can definitely do it again.

    I also need to change the main air vent. I keep seeing people suggestions the Gorton #2 to others. Would that be an appropriate main vent and if so where can I get one? I haven't found one locally after calling around.

    The pigtail was just added to the system, it wasn't there before. I'm not sure if this coincided with the banging. Is there a way for me to figure out if the pigtail is fine or do I need a professional?

    No new setbacks.

    Thank you for the help.

    The trol itself might be bad. You would need to add a 0-3 or 0-5 pressure gauge to know for sure. Probably not a coincidence that there is banging and a leaking pressure relief valve. Both are symptoms of high pressure. You can get Gorton #2 air vents at Where are you located?
  • albertbalbertb Posts: 18Member
    release valve

    Jamie Hall

    For safety reasons, I'll have the steam release valve and pigtail looked at. Can I replace the steam release value myself?

    With the banging radiator all the pipes are in the walls. We are talking one steam pipe, I should have mentioned that! The pitch is back towards the inlet right now.

    I'll get a professional to look at the piping, steam valve and pigtail.

    Thank you again.
  • albertbalbertb Posts: 18Member

    I'll add a 0-3 or 0-5 pressure gauge. How would I know if the trol is bad? Would the pressure jump up and down? It never moves on the 30 which is what I've heard happens with a 30psi guage.

    I'm located in a suburb of Boston. Thanks for your help Bn. I'll likely order the Gorton #2 and hopefully will know if I need to order anything else (specifically the pressuretrol) once I follow the steps outlined.
  • albertbalbertb Posts: 18Member

    Am I reading the diagram correctly that the pipe in the back need to be connected to the top like the arrow I drew in this picture?
  • BobCBobC Posts: 4,983Member
    edited March 2014

    The diagram I have attached is the proper way to pipe a steam boiler, the diagram shows both risers being used which is desireable but small boilers can get by with a single riser. The way your boiler is piped almost guarantees you are producing wet steam, if the boiler header was like the diagram you would be getting nice dry steam. That said if it was not banging before that piping is not making it bang now.

    Your mains contain over 0.4 cu ft of air each and the present main vent is good for about 0.1 cfm. Each of those vents should be replaced with 2ea Gorton #1 vents per main at a minimum, a single #2 would be better but will cost a bit more than 2ea #1s. You can buy Gorton main vents at Note that the #2 vents have a 1/2" male thread and are quite large, make sure you have enough clearance  to mount them.

    Those Home Depot vents are not good, they should be replaced with Gorton, Hoffmans, Ventrites or Maid o mist radiator vents. It's best to vent the mains fast and the radiators slowly, the Home Depot vents seem to always vent at the same rate and that is too fast.

    Is the boiler shutting down on low water during operation or only when you drain it? If it's shutting down during normal operation your return pipes might be partially clogged.

    Let us know how you make out with checking the level of the pipes and that the pigtail is not blocked.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • albertbalbertb Posts: 18Member

    Here are some updates from the last couple of days. I took out the sight cglass, cleaning it out and replaced the rubber. I also flused the boiler twice.

    -Does run the boiler up to steam just mean run it normally or is it a different level?

    Additionally I removed the pigtail and cleared it out. I don't think it was blocked but there was some gunk in there. There was still some banging this morning but it didn't seem as loud.

    I have a steam release valve and two Gorton #1s arriving today which will be swapped out as well. Hopefully by tomorrow I'll have this problem under control.

    I don't know how to test if the pressuretrol is working. Does anyone have any suggestions? Also what should it be set at?
  • vaporvacvaporvac Posts: 1,516Member
    Skim the boiler...

    It might be that flushing the boiler won't get everything out of the system. Try a slow skim and probably more than once. Search Skimming on THE Wall for instructions.
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
  • albertbalbertb Posts: 18Member

    My pressuretrol is set to .5 on the outside and 1 on the inside. The boiler got up to 4 Psi today which is higher than I've heard is acceptable. Does that mean the pressuretrol needs to be replaced?
  • FredFred Posts: 7,983Member
    Have you checked the pigtail?

    Have you checked the pigtail below the pressuretrol to make sure it is not clogged up with gunk? If it is clear, the Pressuretrol probably needs to be calibrated. My Pressuretrol did the same thing. Since I re calibrated it, it operates just as it is suppose to, Cut in at .05psi, Cut-out at 1.5psi (.05 Cut-in plus 1.0 psi differential). Follow this procedure to recalibrate your Pressuretrol or have your service tech do it for you:

    Inside the Pressuretrol, right below the micro switch, there is a pivot arm. At the end of that arm you will see a screw pin that is activated by the diaphragm at the bottom of the Pressuretrol. If you look very carefully at that screw pin, you will see it actually has a tiny (I mean tiny) hex head on it. It takes a .050 hex wrench and you can turn it clockwise (Towards the bottom of the Pressuretrol to decrease the Cut-out pressure or counter clockwise to increase the cut-out pressure (which none of us want to do but who knows, your Pressuretrol may be really screwed up!). Turn the power to the unit off first. You may find the first attempt to turn that screw a little bit stubborn (relatively speaking) because it has some Locktite on it but it does turn. Don't turn to much, a fraction of a turn goes a long way towards getting it adjusted where you want it (not even an eighth turn). You may need to play with it to get it exactly where you want cut out to be.
  • albertbalbertb Posts: 18Member
    Still a problem, slightly different

    I had a professional come and they adjusted the pitch of the dry return. They also swapped out the pressuretrol and skimmed the system.

    I'm still getting loud banging but now it's only near the beginning of the cycle and for a shorter period of time. It lasts roughly 30 seconds to 1 minute but is extremely loud. I tried fully closing the valve next to the loudest radiator but the banging still happens, just right at the valve instead of inside the radiator.

    Could it be that the two Gorton #1s main vent aren't enough to let the air out?

    Is there anything else I can try? The pigtail isn't clogged, the system has been skimmed and the main air vents have been replaced. The system was going up to 4psi when the pressuretrol was broken, now it only gets to 1/1.5.

    Any thoughts or help would be appreciated.
  • FredFred Posts: 7,983Member
    Valve fully opened?

    Are you sure you have that valve fully opened? Water hammer isn't going to be caused by the vents. If the valve is fully opened,It sounds like the pitch of the pipe that feeds the radiator may not be sloped back towards the boiler or the radiator itself is not pitched back towards the supply valve. There is water/condensation sitting in that area and when the steam hits it, you get the hammer.Check the pitch of the radiator, the supply to the radiator, make sure the valve is fully opened 
  • BobCBobC Posts: 4,983Member
    Pipes, valves and vents

    Can you see the pipe in the basement that goes from the steam main to the radiator that is banging? It sounds like there is water trapped in that pipe because it's slope might be bad. If the radiator is on the second floor you might have to lift the entire radiator (both ends) to correct the slope of a pipe you can't see.

    Make sure that radiator valve is all the way open and try a slower air vent on that radiator; as I said earlier the air valves they sell at HD are not very good.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • albertbalbertb Posts: 18Member

    The valve is fully open and the radiator is angled back towards the valve. The entire pipe could have a slope issue somewhere along the way but it runs through the walls from the second floor down to the basement so there is no way to pull it up. I tried raising the radiator to raise the entire pipe from the valve to no avail.

    Thank you for the feedback on the vents not making a difference for this problem.
  • albertbalbertb Posts: 18Member
    re:Pipes, valves and vents

    I'll try lifting the entire radiator higher with the help of a second hand, although I think I've pulled it up as much as possible. I'll do this in the next day.

    I also swapped out the home depot valve with a hoffman air valve.

    I'll also look at the pipe in the basement again to verify the slope and try to figure out where water is getting trapped.
  • albertbalbertb Posts: 18Member

    Although this hasn't changed the plumber told me the cause could be the fact that the pipe that leads to this radiator goes straight up vertically from the main pipe coming off the boiler. Take a look at the attached pictures. Could that be the cause?
  • FredFred Posts: 7,983Member
    edited March 2014
    Not in the wall

    the problem is not likely to be in the wall since that should be a straight drop. It has to be in the short horizontal pipe run from the radiator to the wall or in the horizontal run(s), in the basement, from the main to the riser in the wall. Is this just happening with one radiator or multiple ones? Have you had this problem for a long time or just recently? Has anything changed or any work been done with or around that piping? Are any of the horizontal runs in the basement sagging? They may be slopped right but if they have a sag in them somewhere along the route, that will allow water to puddle.

    It's much better from those radiator runs to come off of the mains at an angle but I have a couple that drop straight down like that also (as originally plumbed 112 years ago) and have no problem with them. That looks like at least a 2" to 2.5" pipe coming off of the main. Are their multiple radiators on that run? If so, it is possible that enough condensate is running back to the main and dropping stratight down into the steam to cause some hammer.
  • albertbalbertb Posts: 18Member
    Vale to radiator

    Water is still filling up inside the problematic radiator even though it's at a big angle now sloping down to the valve. Does this valve look completely open or doe sit need to be replaced?
  • FredFred Posts: 7,983Member
    edited March 2014

    That valve looks like it is only about half open. Is the round disc above the actual brass stop loose? Looks to me like that was originally pressed up in the valve body and maybe has broken loose.Then again, it may be fully open and what I'm looking at is an illusion and is actually the back wall of the valve body. Hard to tell from this pic. After studying the pic some more, I'm pretty sure the valve is fully opened and what I'm seeing is the rear wall of the valve.
  • albertbalbertb Posts: 18Member

    I'll disassemble tomorrow morning and report back. Thank you. This could be causing the water to get stuck in the radiator correct?
  • FredFred Posts: 7,983Member
    Horizontal Pipe

    I am still going to guess that there is a short horizontal pipe under the floor board that extends that vertical pipe and valve away from the wall that is pitched the wrong direction.
  • nicholas bonham-carternicholas bonham-carter Posts: 7,882Member
    Too much water blown up

    The real cause, of your gurgling radiators, I think is due to the improper boiler piping, which is blowing a lot more water up into the mains with the steam.

    The second problem of hissing radiator vents is due to excessive pressure coupled with inadequate main venting. Loud vents are a cry for help from the system. They are also a godsend for the fuel supplier who is supplying you more than you need to heat the house .

    If you can correct the piping, and keep your back-pressure of venting below 2 ounces, and your steam pressure under 6 ounces, then you will have real comfort and economy.

    You will need a 0-3 psi gauge to monitor these conditions.--NBC
  • albertbalbertb Posts: 18Member

    I took the valve in to a plumbing supply shop down the street for a second opinion and they confirmed that it is open. That eliminates the valve as a source for the problem.
  • albertbalbertb Posts: 18Member
    horizontal pipe

    The vertical pipe is about 4" long (guessing) under the floor then it extends horizontally towards the middle of the house where it goes down the basement. I have tried proping the entire radiator up to pull that horizontal pipe up and give it the proper pitch to no avail.

    I'm not sure if this is the case or matters but it seems like the horizontal pipe also connects the bathroom radiator (in wall) on it's way down to the basement.
  • albertbalbertb Posts: 18Member
    Too much water blown up

    I installed 2 Gorton #1 main vent valves. Is there any way to tell how many total I need before I order more from Pexsupply?

    I'll also get a 3PSI gauge to figure out exactly what the pressure of the steam is from the boiler.

    Can you explain how to measure back pressure vs steam pressure? I have the one 30psi valve on the boiler (understanding that it shouldn't go above 2psi) but that's the only one I know of.

    Finally I need to find a good professional in the Boston are to repipe the system. I've contacted one so far but left unsatisfied based on what was charged and the problem not being fixed.
  • teaneckplumberteaneckplumber Posts: 1Member
    Steam Hammering

    replaced steam boiler with 150,000 btu natural gas with 2 tappings on boiler. Did not hear old boiler or system running prior to installing. existing system has one 3/4 condensate return for entire system. House is aprox 1,500 square feet with 2 floors. Someone installed 3/4 copper fin tube baseboard throughout house with vents. homeowner gets banging noise first thing in the morning. no signs of main steam air vents in system and only one 3/4 copper condensate return line into boiler room. we were going to install main steam air vent on condensate returns,pitch baseboards, and main steam air vent in boiler room to help with vaccum. read Dan Holohan's steam book and book recommended installing receiver on condensate return. has anyone used in residental applications or can give more suggestions besides adding steam air vents on return lines and end of main steam headers? according to homeowner system was working with no banging prior to new boiler installing.
  • SWEISWEI Posts: 7,356Member
    New project, new thread

    unless this is about the original poster's system.
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