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Munchkin boiler leaking from heat exchanger

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SFsteve
SFsteve Member Posts: 11

I have a MC-99 Munchkin Contender mfg date 1/2007 NG. I am a homeowner and not a pro.

The boiler serves my closed loop radiant heat system and the hot water tank.

2 months ago I had a small drip from the base of the heat exchanger that found it's way into the contol board and fried the board. I replaced the combustion blower as the oringinal error code was related to excess blower speed. That wasn't the fix, and so I replaced electronincs with upgraded board, control and all worked great. Tightened a few screws and leak disappeared…for awhile.

Now I have a bigger leak, about a cup every 15 hours. Dripping from base of heat exchanger unit. Caught it before it ruined the new board.

Boiler is operational, heating and working well EXCEPT for the leak.

I'm wondering if I need to replace heat exchanger. How do I know. What else could cause the leak? My drain line from HE to collection cup seems clear and I have condesate dripping from line outside.

Obviously, I am trying to avoid a NEW bolier. The bolier seems like a relatively simple systems and with a new blower, electronics already installed, I'm just one part away from a rebuild?

I also wonder about recommended setting. Setpoint max is 180, should it be lower? Trigger is set a 15 but can be 30.

Like what else could go wrong?

Thanks for any help. Really truly appreciate it.

Steve

Comments

  • Ironman
    Ironman Member Posts: 7,377
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    I'd highly recommend that you replace it with a new boiler.

    The Munchkin is obsolete and there are better designs now available.

    Look for something with a fire tube heat exchanger.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    SFstevefenkelSuperTech
  • kcopp
    kcopp Member Posts: 4,438
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    I tried 1 time to fix one. Lasted 3 months.

    Ended up w a new boiler.

    The outside of that HX is plastic. It wasnt the best attempt for HTP.

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,033
    edited March 2023
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    It looks like condensation coming out of the burner door; maybe a clogged condensate drain.

    Agree with the others even though you've spent a lot of money already - replace the boiler.

    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
    SFsteve
  • SFsteve
    SFsteve Member Posts: 11
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    I understand the boiler is old. But it is working great except for leak. Do you think the flue pipe is running down the top of the HE, becasue I don't see anything externally.

    I'm in Northern CA, any recommended boiler brands?

    Thanks,

  • mattmia2
    mattmia2 Member Posts: 9,734
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    How often has this been serviced?

    Ironman
  • SFsteve
    SFsteve Member Posts: 11
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    3-4 times since install. last time in 2019

  • kcopp
    kcopp Member Posts: 4,438
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    See if you can pinpoint the leak…

  • Alan (California Radiant) Forbes
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    IBC makes a good boiler. Same with Lochinvar. They are both well represented here in the Bay Area.

    I had a 2007 Munchkin in my basement until it started leaking last year and many of my customers who own Munchkins are starting to have problems.

    Send me a PM if you want to talk.

    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
    kcopp
  • SFsteve
    SFsteve Member Posts: 11
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    So, thanks to Alan Forbes I took another look for the leak. I now beleive it's coming from the top of the unit. See pics.

    This is the water pressure switch. I rules out a leak from the vent tube shown.

    I'm guess its the o-ring under the adapter and or the o-ring under the water pressure switch.

    Thoughts? AND THANKS

  • mattmia2
    mattmia2 Member Posts: 9,734
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    My guess would be the o-ring where the pressure switch snaps in to the hx. My car has a similar connection on one of the radiator hoses and you have to replace the o-ring every time you take the sensor out or it leaks.

    SFsteve
  • Alan (California Radiant) Forbes
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    Yes, it could be that o-ring;; an easy fix.

    Is there anything above it that could be dripping down?

    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
  • JUGHNE
    JUGHNE Member Posts: 11,074
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    Did you say you had water coming out of the cond drain hose even if not firing?

  • SFsteve
    SFsteve Member Posts: 11
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    Jughne -

    Not sure what you're asking. The main hose that drains into cup under boiler? I haven't looked at that when it's not firing? What would that mean? if there was water draining when the system was off.

    Leak seems to be on top. I'll replace o-rings but i don't see a leak at the connector but near it. That's why I thought the leak might be from the vent tube.

    I have another concern about the clip connectors on the supply inlet and outlet where they meet the HE on the bottom. One is fairly corroded. Can this 'blow' if not replaced?

    Here's a pic or two, as a pic is worth a 1000 words as they say.

    I oreder the o-rings for the water pressure switch and the o-rings and clips for the supply and outlet tubes. Should have everythign in house on the 5th and then it' game day. Any recommendations on the grease to use on the o-rings, I've see some say silicone and others use plumbers heatproof grease?

    I really appreciate all the advice and input here.

  • hot_rod
    hot_rod Member Posts: 22,244
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    Just a little lube to slide it together, plumbers stem lube should be fine.

    I had a Baxi that started leaking on connections like that, after 15 years of service. Hopefully the composite body is not grooved or damaged.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    SFsteve
  • SFsteve
    SFsteve Member Posts: 11
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    Wanted to close this chapter about my experience with my 16 year old Munchkin MC99 boiler.

    After a couple of months replacing this and that, I have completed repairs and the unit is working perfectly. Total cost of parts was right about $2,500. $400 of that to replace electronics that had shorted due to leaks in the system. If the maintenance folks had been a bit more detailed that would have been avoided.

    The exhaust fan needed to be replaced. And ultimately the HE was too brittle and cracked to work with. I had a leak at the top where the pressure switch is as well as with the return pipe on the bottom of the HE. These leaks found there way into the control box (horrible location for it) and shorted the electronics.

    Note to self, inspect boiler quarterly for leaks.

    The process was quite easy as all parts were simple to install, including the HE which took me, a novice, just 2 hours at a slow pace.

    I've included pics of the completed job. Nice and clean, no drips, no leaks, no noise. I think it was actually worth the time and effort to rebuild the boiler rather than buy new. Although, I suppose some would argue that the MC99 isn't as efficient as newer models, but at the same time I've saved a couple of bucks and repurposed equipment.

    You can compare the attached pics to the previous ones for fun.

    Thanks to all who commented and offered words of wisdom, really appreciate it.





  • mattmia2
    mattmia2 Member Posts: 9,734
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    I'd keep a very close eye on that exhaust outlet and make sure I had a low level CO detector. That plastic isn't supposed to be that color.
    IronmanSuperTech
  • Ironman
    Ironman Member Posts: 7,377
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    Have someone do a combustion analysis: from the color of that PVC, it looks like it’s over-firing.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    mattmia2SuperTech
  • hot_rod
    hot_rod Member Posts: 22,244
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    What temperature are you running it at? I’ve seen the flue turn color like that when they run 180f all the time.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GGrossmattmia2Ironman
  • bigboy101
    bigboy101 Member Posts: 1
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    I have the exact problem with it leaking at the top near the pressure switch. My MC99 is about 10 years old. I'm currently getting a "PRO" error code which means low pressure. It is sitting at around 10PSI. I can get the boiler to work by power cycling it. It will start to heat and the pressure will rise to about 15PSI. But then after a day or so, the low pressure switch will trigger again. Do you think replacing the pressure switch assembly and O-rings will fix my problem? Or would I need to replace the HE (7500P-014 Composite Module) ? I'm wondering if it is cracked somewhere but I cannot see any cracks near there.


  • hot_rod
    hot_rod Member Posts: 22,244
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    A simple thing to try replacing the O ring. Use some fine emery cloth or a pot scrub pad to clean the brass well where the ring seal.
    Stem lube on the new assembly also, or silicone grease.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    HomerJSmith