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Question about heat exchanger 'sweating'

My question regards a Munchkin boiler, the m80 that is 17 years old and is still working. The Munchkin has been heating my 1200 sf addition and has 3 zones. My latest technician who "serviced" the unit, put his hand on the heat exchanger and showed me that it was damp. He said that there was a pinhole leak in it and I would need to replace the whole unit at considerable expense. As many know, the Munchkin does not have many available parts. In the process of trying to find a contractor to get me some estimates (very difficult), the latest contractor suggested one of his techs to test the boiler and actually see if the heat exchanger has a leak, or it is supposed to be damp on the inside. Maybe I don't need a new boiler. He said he is happy to sell me a new boiler and the install. Any thoughts on this would be appreciated.


  • Jamie Hall
    Jamie Hall Member Posts: 18,951
    I'll bet he's happy to sell you a new boiler.

    Find out if you need one first. Are you adding any water to your system? That's the simple test...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 9,765
    With the boiler off, you could watch the condensate drain line to see if any water is coming out. Put the hose in a bucket and maybe wait overnight or so.
    The pressure should be 12-15 PSI. You could bump it up to 25 just for the test.

    Or if there are isolation valves to the boiler, you could close them and see if the boiler pressure falls....if there is a pressure gauge on the boiler itself when it is isolated from the system.
  • clammy
    clammy Member Posts: 2,740
    I would check the heat exchanger and also the condensate to ensure it’s not clogged but at 17 years old she getting close to replacement being most wall hung boiler have a life ex of any where from 10 to 15 years w proper maintenance. If you had good luck w no issues over all those years I would start budgeting and start looking for Botha new wall hung and a installer to do it right . I have a munchkin m80 bout 13 or14 years old and I’m getting ready to replace most likely w a htp water tube elite much better modulation ratio then the original and I feel water tube are easier to clean the heat exchanger over a fire tube which verybody I know loves because they state they don’t need cleaning self clean8ng im not buying it. Plus if fire tubes where so great not arguing but how come the big V isnt making and selling them , and I think not sure but I think the water tubes have a lower mod rate not much but a bit lower then fire tube . It s quite easy to remove the front burner plate and plug the condensate line and fill chamber w water and see if the bottom is leaking it happens Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • PerryHolzman
    PerryHolzman Member Posts: 234
    My memory (perhaps incorrect) from when I researched boilers in 2007 for my house is that the Munchkin of that era used o-rings to seal the various tubes to the header on the heat exchanger. IF that is true (???), then your only problem may be degraded o-rings. IF So (???) you should be able to find replacement o-rings from many companies and change them with a careful disassembly and reassembly. Be very sure to match the material and size, and use the proper lubricant.

    Of course, many companies will only want to sell you a new boiler.

    Since you have a condensing boiler, the HX is normally moist, unless it has been dried out.

    I rate the technicians method that you described more likely towards the scam end of things instead of the correct method of determining leaks.

    Hope this helps,

  • unclejohn
    unclejohn Member Posts: 1,757
    My money is on the condensate drain being clogged. Easy way to clear is too shut off the gas to the boiler, block the exhaust pipe, disconnect the low voltage wire harness from the fan and start the boiler. This will pressurize the heat ex and blow out the drain. You need to have someone outside with a rag in the ex. pipe.