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Munchkin Combustion Reading

We just cleaned a Munchkin 140M, Rev. 2 boiler and did a combustion analysis. No matter how far we turned the adjustment screw, we couldn't get more than 8.4% CO2. We even replaced the burner. Normally, it's not a problem to dial in and can easily get to higher numbers than what you want, i.e. into the 10-11% CO2 range.

The carbon monoxide level was fine: 25-50ppm.

Any ideas? Bad gas valve?
Often wrong, never in doubt.

Comments

  • SuperTech
    SuperTech Member Posts: 1,687
    Maybe an air leak somewhere? Bad gaskets on the igniter or flame sensor? 
    rick in Alaska
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 2,965
    edited November 2020
    Bad gaskets on the igniter or flame sensor?
    We replaced both with new gaskets.
    Often wrong, never in doubt.
  • JUGHNE
    JUGHNE Member Posts: 8,927
    How about the rope gasket on the door?
    Crack in the door or sight glass?
    There is a gasket behind the burner but can't see extra air showing up on that.
  • Thanks, @JUGHNE.
    We replaced the rubber burner gasket as it came with the refractory.
    I spoke with tech. support earlier today and they said that it's not that hard to permanently throw off a gas valve. One delayed ignition can do it.
    Often wrong, never in doubt.
  • SuperTech
    SuperTech Member Posts: 1,687
    Let us know how it goes with the new gas valve.  I haven't seen this problem yet, but I see enough of these troublesome boilers that its probably just a matter of time before I do. 
  • I service a couple hundred Munchkins, including the one in my basement . For the most part, they have proved themselves to be long-lived and reliable with parts readily accessible. They were the first reliable mod-con (remember Hydrotherm Pulse, Glowcore, and Heatmaker) assembled in the US.

    @SuperTech: Same here: I've never seen this before.
    Often wrong, never in doubt.
    Zman
  • HomerJSmith
    HomerJSmith Member Posts: 1,362
    Maybe you have to adjust the Offset on the gas valve. I have the paper work on that or you can go to HTP forum and download it.
  • lchmb
    lchmb Member Posts: 2,997
    LP or NG? pressures acceptable?
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 2,965
    edited November 2020
    Maybe you have to adjust the Offset on the gas valve. I have the paper work on that or you can go to HTP forum and download it.
    I try to leave the offset alone except on low fire. Can you give me the link to the HTP forum?

    LP or NG? pressures acceptable?
    NG. Pressure is ~7" and hardly budged on ignition.
    Often wrong, never in doubt.