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Erratic Munchkin Boiler

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MikeG
MikeG Posts: 173
in THE MAIN WALL

Been awhile since I've posted. I have a Munchkin 80m boiler on LP, 925 controller, Amtrol TD1L indirect for domestic, 3 zones finned baseboard and a small radiant zone all thru Taco SR 506 relay with pumps. On a call the boiler fails to ignite all the time. Fan runs it tries multiple times, then locks out. It does not show any error codes. Spark gap is correct. If it does fire it doesn't reach high limit and shuts down, then tries to restart and goes to lockout. If I turn power off and wait it may fire again. Any ideas or what to check is appreciated. Thanks Mike

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Posts: 12,854
    edited September 27

    Flame signal

    Look closely at the failures. Is there a flame and then it goes off?

    Since it has been some time since I worked on a Munchkin, can you tell me: is there a spark to the main burner or a spark to a pilot?

    If it is a spark to a pilot, look to see whether there is a pilot flame that comes on, goes out, and then tries again. If the pilot flame appears and then goes out right away, the flame signal is not getting through to the ignition control.

    Here are my steps for the repair:

    1. Clean the flame sensor.
    2. Verify ground connection from sensor to control ground. (ask me how if needed)
    3. Replace the flame sensor.
    4. Replace the sensor wire.
    5. Replace the control.

    That goes from lowest cost to highest cost until you get it to operate without a failure. Hopefully just polishing up the flame sensor with emory cloth or steel wool will solve the problem

    If there is NO FLAME on trial for ignition, then we look in a different direction.

    Edward Young Retired

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

  • JUGHNE
    JUGHNE Posts: 11,644

    Has the front cover been taken off and the inside coils cleaned?

    MikeG
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Posts: 4,874

    Check the condensate path. I bring an air compressor with me on Munchkin calls to backflush the condensate drain as the trap often gets clogged after all those years.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    GroundUp
  • plumbworker
    plumbworker Posts: 34

    like others have stated. Verify combustion chamber cleanliness, burner condition, proper condensate flow, gas pressure, flame signal while running (d7) in the status menu. Does the burner light off every time and drop out?

  • HomerJSmith
    HomerJSmith Posts: 2,833
    edited September 29

    Ed, it has a direct spark ignition or a HS ignition if a high altitude boiler. I was taught to use wet & dry sandpaper as emery cloth leaves a coating on the electrodes.

    If a spark ignition, the probe has a spark gap that should be two silver (ha! that'll be the day) quarters placed together, wide.

    When you clean the combustion chamber, replace the old burner tube gasket with the new thicker one and make sure the four screws connecting the tube to the front plate is screwed really tight. Rectification & flame proving happens thru those four screws.

    Do a combustion analysis on it.

    e

  • MikeG
    MikeG Posts: 173

    The combustion chamber is clean. The spark and rectification probe were cleaned. Checked all wiring spade lugs, condensate ok. When I clean it I replace all gaskets and target wall even if they look good. I will check the screws. This happened once back in June. So yesterday I turned off power, powered it back up and it works now. Electrical gremlins??? I will relook everything.

  • EdTheHeaterMan
    EdTheHeaterMan Posts: 12,854
    edited September 28

    So what do the nuts and bolts and sheet metal screws look like that are connecting all the parts around the burner and the flame sensor? If they are a little rusty there may be a problem with the chassis ground that is the main conductor of electricity from the flame to the control module ground connection. That flame signal is not all that powerful and a little corrosion can certainly make that path a higher resistance than it was when it was brand spankin' new.

    I have fixed this by fixing a copper wire (green ground wire) directly on one of the screws that hold the flame sensor rod in place, and running it to the ground connection on the ignition control.

    image.png

    If you look close at this boiler, someone has already done that on the other screw that holds the electrode/sensor.

    Edward Young Retired

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

    HomerJSmith
  • MikeG
    MikeG Posts: 173

    Thanks Ed,

    The spark electrode and rectification probe screws look good. It doesn't hurt to run an additional ground. Had that kind of issue on my sons Burnham boiler. The pilot ground would corrode and wouldn't prove the pilot. Without doing anything it's working right now. For how long who knows. I will go in and clean up everything to sure. Thanks

  • plumbworker
    plumbworker Posts: 34
    edited September 29

    Does flame drop out after ignition? What is the flame current read out during burner operation 925 ideally is 3.5ua i think the minimum is around 1.2ua (its been a while since i dealt with service on the munchkin buts its coming back) the 925 should output 48vac to the flame sensor. Anything below that will cause flame drop outs.. and will likely require a 926 upgrade..

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