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Munckin 140MR2 F09, condensate backup

I'm seeing an F09 code due to water not draining from the combustion chamber. Water backs up across the entire chamber, so I'm pretty sure it's not due to a clog in the chamber itself.

To clear the line I applied a vacuum to the condensate drain, and that seemed to draw air through the combustion chamber at least for a while. But after a few minutes it is clogged again, and no amount of vacuum will clear it.

Is there some other way to clear this line? Like with a snake? Maybe I could alternate blowing air into the condensate drain line and vacuuming? I don't have a mental model for how water leaves the combustion chamber before arriving at the drain.

Thank you,


  • hot_rod
    hot_rod Member Posts: 22,327
    Did the boiler settle or start to lean to the front for some reason. That can prevent condensate from draining completely. Where does the drain tube go? Into a neutralizer? Check for obstructions from the drain port to the final drain location. A clear vinyl hose works well for keeping an eye on the tube plugging. Many are done with PVC pipe.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HomerJSmith
    HomerJSmith Member Posts: 2,476
    edited November 2022
    When is the last time you had a combustion chamber cleaning? Looking thru the sight glass do you see any water lines on the back refractory? Water in the combustion chamber can interfere with the rectification.

    Most F09 error code is because the burner tube is not tight to the front plate, the four screws have loosened thereby not providing a good ground for rectification because the burner gasket is failing. The new burner gaskets are much sturdier.

    I clean Munchkins about every 3-4 yrs and it take me about 2 1/2-3 hrs to do the job right.
  • dafoster78
    dafoster78 Member Posts: 2
    Hi Bob and Homer,

    Thank you for your comments. It turns out, there was a major clog where the drain line exits the boiler, and my shop-vac couldn't clear it. All I had to do was remove the rubber hose from the bottom of the boiler and clean it out.

    Thanks again,
  • HomerJSmith
    HomerJSmith Member Posts: 2,476
    Sounds like coffee grounds. I would say a cleaning is definitely in order along with a combustion analysis.