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Munchkin Explosive Sounds

We are experiencing occasional explosive like sounds from our Munchkin water heater. We can see a quick muzzle flash when it happens...does anyone have experience with this?


    JUGHNE Member Posts: 10,915
    How old is this? When was the last time the boiler was opened and cleaned?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 6,763
    The explosive sound and the muzzle flash is a result of an ignition problem. Gas is entering the combustion chamber and igniting a little late.

    When was the slat maintenance visit from a professional?

    Remember a repair is not maintenance. Fixing a circulator problem or a thermostat problem is not a complete maintenance service. The ignitor may be loaded up with some deposits from the combustion process and the flame sensor may also need cleaning or replacing. Look in the back of the Installation Manual for your appliance. Read the part titled Maintenance.

    It is amazing what you can find in the manual.

    Respectfully Submitted
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • fenkel
    fenkel Member Posts: 162
    You need to have your system cleaned correctly, which would include the replacement of ignitor and flame sensor ... then a proper gas analyst performed...
  • HomerJSmith
    HomerJSmith Member Posts: 2,311
    edited January 2021
    Jughne and Ed are right. After a good maintenance process and you still have the problem, look at the fuel delivery path and the ignition module and the spark cable. Yes, have a combustion analysis done by a tech with a recently calibrated CO meter.

    Model and year are helpful.
  • tim smith
    tim smith Member Posts: 2,708
    my guess is the venturi will be toast or burner has a hole in it. Regular cleaning a must on Munchies.
  • Geosman
    Geosman Member Posts: 23
    I've seen them backfire as you describe and discovered that the condensate trap was blocked causing condensate to back up inside the boiler wetting the refractory insulation behind the burner plate. Damp insulation allows the ignition arc to the refractory rather than jump the gap on the ignitor causing a delayed ignition with the chamber filled with gas before it ignites. It's pretty scary and makes the entire boiler jump like it was a pumpkin chuckin spud gun. I would start by shutting off the gas and disconnecting the gas valve and blower wiring connections. With the gas valve piping free and wire connections off, the front cover with gas valve blower and entire face should pull away cleanly. The chamber needs to be brushed and flushed along with flexing the condensate trap to clear sediment. Inspect the ceramic refractory around the ignitor and scrape away any that may be too close if it is slightly out of position. Check and clean the flame sensor and be certain the ignitor spacing is no further than the thickness of two quarters. If you have a hot air gun, dry the refractory around where the ignitor enters and reassemble. It should fire off without the delayed ignition and without backfire.