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Flame inside burner tube

I have a 20+ year old Smith GB200 gas fired steam boiler with 5 burners. Occasionally, when the boiler fires, the flame is inside the burner tube closest to the gas valve. It has never been inside any of the other burners. If I turn off the boiler, let it sit until the controls settle out (i.e., vent damper) and turn the boiler back on, the flame does not go into the tube.

I wire brushed all burners, except the one with the pilot, disassembled the piping from the gas valve to the burners and made sure it was clean, and reset the gas pressure. I did not measure the orifices to check of there is any size difference. I made sure the end of all burners at the orifices are in the same place to eliminate positioning as a variable.

I don't keep a manometer connected to the gas valve outlet, so I haven't been able to see if or how much gas outlet pressure varies. I don't live at the house, so I'm not inclined to leave one installed for any length of time, even if I had a shutoff valve between the gas valve port and the manometer.

In talking to the manufacturer's tech support person, he suggested I try reducing the pressure a little bit to see if that eliminates the problem. Technically, I am unable to explain to myself why reducing the pressure would move the flame out of the burner. It seems to me decreasing it would feed the gas slower into the burner letting the flame occur closer to the inlet.

The rep also said it's a hit or miss guess on whether reducing will work.

The air adjuster is fully open in all 5 burners.

Does anyone have any suggestions?


  • STEVEusaPA
    STEVEusaPA Member Posts: 5,977
    Don't change the gas pressure without a manometer and an analyzer (full combustion test).
    JUGHNE Member Posts: 10,315
    Sometimes a partially plugged gas orifice might cause that.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 809
    I do have a manometer, don't have a gas analyzer. Probably too expensive for me to justify buying. Hmm. Gotta figure that out. I haven't been impressed with the HVAC company I have been using...too interested in trying to up sell me. I'm not sure how much of an effect a couple of 0.1s an inch of water pressure would have on combustion analysis. Perhaps, the condition of the flame could be an indicator.

    At one time I thought maybe there was static electricity/dust building up on the orifices, so I now use a piece of copper wire (soft material) and put it in each orifice just about every time I am at the house. Another factor, which is unproveable is that I have been working on repairing and painting a plaster stairway and have been going in and out of the basement many times during the day, probably disturbing the dust, etc. that is on the floor of the 90+ year old house.
  • mattmia2
    mattmia2 Member Posts: 7,194
    You need someone with combustion analysis and draft measurement tools and knows how to use them, you need to make sure the passages in the boiler are clear and the vent is clear and drawing properly, then you need to set up the combustion properly with an analyzer.
  • ethicalpaul
    ethicalpaul Member Posts: 4,208
    My old Utica would do that occasionally, with a whistling sound that was noticeable while it was doing it. I think it did it when I had lowered the valve pressure a bit. A well-respected steam pro who saw it indicated with a shrug that it can happen sometimes.

    See what the pressure is currently set at and if it varies from what's specified on the boiler plate, I can't imagine the harm in putting back to spec to see if that changes anything.
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
    HVACNUT Member Posts: 4,868
    What brand and model gas valve?
    Is it a Slow Opening or Step Opening valve, or does it go from 0 to 3.5" right away?
    EBEBRATT-Ed Member Posts: 13,146
    I have seen that happen as well. Sometimes you chane the gas pressure a little or tweek the air do a combustion test check and clean the orifices
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 809
    I am not at the house, but the manual says NG VR8200H1129. I had the boiler installed and the gas valve is original. I'll check the next time I am there. I don't see anything in the manual discussing slow or step opening.

    The primary air shutters have always been full open. If there is yellow flame indicating too little air, since more air can't be "added", my guess is the gas delivery pressure may be too high.

    Perhaps, that is consistent with my other comment about reducing pressure if the flame is inside the burner.

  • SteamingatMohawk
    SteamingatMohawk Member Posts: 809
    I thought it's a Honeywell, but on the Supply House web site it says that model number is Hydrotherm.

    I also found on the www that it is supposedly slow opening.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 809
    Gas pressure was adjusted in early 2019 to 3.5, hasn't been checked since then.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 809
    I finally got to the house and did two things.

    First, I bought a drill bit the size of the orifice. The bit fit nicely in the 2nd through 5th orifice. It got stuck in the first one, which is the one with the flame inside the burner. I removed the orifice and used the bit to remove whatever was causing it to bind in the orifice.

    Second I checked the gas pressure, which was 4.2. I adjusted it to 3.5.

    Since then, I have no evidence the flame has been inside the burner.

    Easy fix, if you have the right tools.

    See my other discussion on gas valve pressure drift.