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Clanging Boiler on start up

gfrbrooklinegfrbrookline Member Posts: 277
My boiler makes two loud of clangs within 20 seconds of firing from cold. It's a Burham V904A with a Beckett gas burner. I don't think it could be a water hammer in the pipes because all of the pipes are cold and there is no air moving through them since the boiler water is cold.

Is this likely just the thermal expansion of the boiler or should I be concerned?


  • FredFred Member Posts: 7,327
    Pictures of the near boiler piping would help us help you. Not likely thermal expansion if it is cold. If it is hot enough for expansion noises, it is hot enough for steam to be hitting a pool of water, maybe in the header. Do you have an equalizer and is the header pitched towards it so that water doesn't pool in the header?
  • gfrbrooklinegfrbrookline Member Posts: 277

    I know the A dimension seams short but it is actually 23" from the water line. The take off is 4". I will agree before anyone says anything that the installer should have used 2 take offs from the boiler. They wanted to reuse the header, if I knew then what I know know I would have had them scrap it and install a drop header.
  • FredFred Member Posts: 7,327
    WOW, a lot to try and see there. Is this a counter flow system? It looks like the mains are lower at the boiler than they are as they travel away from the boiler, but I also think I see where a dry return comes back to the boiler and then drops to the boiler.
    If it is a counter flow, I don't see any drips, into a wet return, right after where the mains connect to the header. That is likely your problem. If it is suppose to be a parallel flow and each main has a dry return at the far end of the main that drops, at some point to the floor and enters the boiler, then the installer pulled your mains down to connect to the header. That is a problem as water would run back down into the header
  • gfrbrooklinegfrbrookline Member Posts: 277
    It is actually a parallel system, two mains, 75' each. There are dry returns on each end as well as two returns for the step risers that tie together about 4" above the floor. The main vents are at the end of the dry returns about 18" before they drop down to wets because there is no access to the end of the mains since they are above a finished ceiling in the basement unit. The hartford loop is textbook.

    The boiler also has a hot water loop for the basement unit that feeds off a heat exchanger and two feeds off the back of the boiler that heat two 80 gallon DHW indirects. It sounds like a lot but it works quite well, we have had this set up since 2005 without issue.

    The vaporstat, mercury, is set to run between 14 and 6 oz confirmed by a 1-3psi gauge and it rarely ever runs more that one cycle.

    You can see the amount of main venting I have. The radiator vents are a mix of Gorton No.4, No.5's, 1 No. 6 on the largest radiator in the farthest unit from the boiler and several Ventrite #1's in the two units directly above the boiler. The 10K sq. ft. building with 7 units is balance within 1 degree, it took me years and many fights with unit owners but everyone is happy now.
  • FredFred Member Posts: 7,327
    So where does the bangs seem to come from? From the actual boiler or from a pipe near/around the boiler? It should not bang.
    It's not the flue damper is it?
  • gfrbrooklinegfrbrookline Member Posts: 277
    Here are pics of the returns turning down to wet and the hartford loop.

  • gfrbrooklinegfrbrookline Member Posts: 277
    The flue damper is fixed or at least it appears to be. I have a draft enducer on top of the chimney that kicks on right before the boiler fires, but the clang seams way to loud to be coming from the draft pipe. It doesn't sound like it is coming from the boiler or the header. It doesn't make sense for it to be coming from the header since there is no velocity coming out of the boiler when the water is still at 160 degrees.

    It is colder today and the boiler has kicked on twice since I have been home. It still makes the clang but with the pipes being warmer between cycles it is much quieter and on the last cycle only clanged once at start up.
  • FredFred Member Posts: 7,327
    Is it from a pump or check valve on the hot water loops?
  • Jamie HallJamie Hall Member Posts: 9,383
    I'm suspecting an expansion noise very near, but necessarily in, the boiler. These can be very hard to track down. If it should happen that you are next to the boiler next time it fires up, you might be able to locate it better. Might even put a hand on the header and see if you can feel it kick when it clangs, for example...

    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
  • gfrbrooklinegfrbrookline Member Posts: 277
    Sounds like the way I use to tune my old car. It's amazing what you can figure out with a long screwdriver. Too bad the younger generation can't figure anything out unless you can plug it into a computer.
  • gfrbrooklinegfrbrookline Member Posts: 277
    @Fred the clanging only happens when the boiler fires for steam.
  • FredFred Member Posts: 7,327
    edited January 8
    I suppose it could be one of the side panels or the top panel on the boiler that pops in or out as it warms up???
  • gfrbrooklinegfrbrookline Member Posts: 277
    I lowered the water level by an inch and all quieted down. I am guessing the lines he drew on the site glass were too high and water was collecting in the header? The level is much closer to the boiler manual now but I suspect my feeder may be mounted a little high.
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