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Very fast Carbon Soot Build Up on Boiler flame sensor

Prevch
Prevch Member Posts: 106
edited January 2021 in Radiant Heating
I had a Utica Mac205 Combi Boiler installed in 2018. When it works, it works fine, but every couple weeks to a month during heating season, the boiler kicks off and won't come back on until I take out the flame sensor and sand / clean it off from all the carbon / soot build up on it. I just did it yesterday actually.

I cannot seem to figure out what is causing this. I had my propane company come out and test my pressures and replace my regulator. They said it is all good. I have 3/4" pipe (the kind that is black plastic on the outside but metal on the inside) running to the boiler from the regulator. I have my propane company and my heating guy call to ensure that the line was big enough and not too long and they both said that I should have more than enough pressure. We even turned the pressure up on the regulator. Boiler calls for 10 - 15 lbs. I think we turned it up from 11 to like 13 or something in that neighborhood.

So I am in the uncomfortable situation of the heating guy swearing up and down that everything is right and the propane company swearing up and down that everything is right. We have dealt with this for years now and I have no idea what to do. Anybody have any ideas?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 24,862
    OK so your pressures are fine -- but has anyone checked the draught and air/fuel ratio? If I were a betting man, I'd bet on something being off there.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HVACNUTdelta TLS123
  • HVACNUT
    HVACNUT Member Posts: 6,332
    The heating guy needs to do more than swear up and down. Swearing sideways won't help either. He needs to put his combustion analyzer on and see what's what.
    EdTheHeaterManMaxMercyLS123
  • Prevch
    Prevch Member Posts: 106
    Jamie Hall said:

    OK so your pressures are fine -- but has anyone checked the draught and air/fuel ratio? If I were a betting man, I'd bet on something being off there.

    Thank. I will ask if he can look into that.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,386
    If it ain't the Fuel, then it's the Air.

    And swearing on the Diagonal could be helpful in this case. I'm kind'a leaning to the NorthEast

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    MaxMercyLS123
  • Prevch
    Prevch Member Posts: 106
    HVACNUT said:

    The heating guy needs to do more than swear up and down. Swearing sideways won't help either. He needs to put his combustion analyzer on and see what's what.

    I will ask him to do that. Thank you.
    EdTheHeaterMan said:

    If it ain't the Fuel, then it's the Air.

    And swearing on the Diagonal could be helpful in this case. I'm kind'a leaning to the NorthEast

    LOL Thank you!
  • HomerJSmith
    HomerJSmith Member Posts: 2,635
    11" of Water/Column is standard for LP input to the gas valve. It sounds as if your combustion is off, too rich.

    Have some one do a Combustion analysis on your boiler with a recently calibrated CO meter.

    Altitude has a lot to do with proper combustion.
    delta T
  • Prevch
    Prevch Member Posts: 106
    HomerJSmith said:

    11" of Water/Column is standard for LP input to the gas valve. It sounds as if your combustion is off, too rich.

    Have some one do a Combustion analysis on your boiler with a recently calibrated CO meter.

    Altitude has a lot to do with proper combustion.

    I will have them do that. Thank you!
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,488
    @Prevch

    When a gas flame makes soot it is usually caused by the flame being too rich....to much gas or a shortage of air

    Also make sure that the burner does not have the wrong orifice. Even the factory screws up sometimes.

    Check your air intake and flue outlet for debris, birds nest etc.
  • Prevch
    Prevch Member Posts: 106
    EBEBRATT-Ed said:

    @Prevch

    When a gas flame makes soot it is usually caused by the flame being too rich....to much gas or a shortage of air

    Also make sure that the burner does not have the wrong orifice. Even the factory screws up sometimes.

    Check your air intake and flue outlet for debris, birds nest etc.

    I will do that. Thank you
  • woodrow
    woodrow Member Posts: 40
    I believe that boiler uses the same orfice for propane or natural you have to make sure on start up it knows its propane you need to do a combustion test i know the new one does not sure about 2018 model
  • Prevch
    Prevch Member Posts: 106
    woodrow said:

    I believe that boiler uses the same orfice for propane or natural you have to make sure on start up it knows its propane you need to do a combustion test i know the new one does not sure about 2018 model

    Yeah I did make sure it was set to propane so that should be good to go.
  • Prevch
    Prevch Member Posts: 106
    Hey everyone thank you for your replies. I have attached a photo of what appears to be two valves on the exhaust / intake pipe on my boiler. The one labeled air I turned all the way to the left (it was in the middle) assuming that all the way left is the open position for more air intake (so it would not run as rich) is that correct? The one labeled flue is set in the middle and I did not move it. Should I adjust the flue one as well? Any advice?



  • Jamie Hall
    Jamie Hall Member Posts: 24,862
    The only way to adjust a burner is with measuring instruments which can determine the correct gas pressures, intake and exhaust draught, and gas flow. There is no other way to do it -- by eye isn't going to work, by guess and by golly isn't going to work.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Prevch
    Prevch Member Posts: 106
    Jamie Hall said:

    The only way to adjust a burner is with measuring instruments which can determine the correct gas pressures, intake and exhaust draught, and gas flow. There is no other way to do it -- by eye isn't going to work, by guess and by golly isn't going to work.

    OK thank you
  • Prevch
    Prevch Member Posts: 106
    Hi Everyone just to update you -
    We got to the point where even cleaning the flame sensor would not work. The Boiler would not even ignite even though we had spark on the igniter. That being said, we think we figured it out and it was related to the build up on the flame sensor.

    It appears that when the boiler was originally installed, it came with a faulty gas valve from the factory. It was letting way too much gas into the combustion chamber when it was calling for heat and just got continually worse over the years.

    When we replaced the gas valve, it fired immediately. We measured the gas pressure and it was quite a bit lower than it was before when it would not ignite. In other words, prior to changing the gas valve, when the boiler fired, it was running too rich. It got to the point where it just couldn't even fire because the valve just kept getting worse.

    Hopefully, now that the gas valve appears to be working as intended, we should not have that issue with build up.

    We did analyze combustion and everything came out good now.

    Thank you for everyone's help.

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