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high temp cutout during Domestic wtr heating w/Munchkin

Recently (today) my 10yr old Munchkin is cycling off on high temp when it is in Domestic wtr heating mode. Something is causing the 'modulation mode' to cease functioning and it quickly soars to 200deg and shuts off. Any Minneapolis technicians willing to lend a hand/advice?
Mark in Minneapolis


  • Zman
    Zman Member Posts: 7,433
    What type of indirect do you have? It may be calcified. Do you have circulation through the exchanger? Try feeling the pipes at the begining of the cycle.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • icesailor
    icesailor Member Posts: 7,265
    That's a good thing to check, but also keep in mind that you may not have any idea of how fast the flow is through the coil. Let the tank temperature drop way down. Let the boiler input to the coil return to warm. Feel the supply so that it is cool to the touch. Turn on the boiler, Notice how fast the hot water comes out of the boiler and gets to the tank, and how fast and hot it comes back. If it is slow to come back or quick to come back and super hot as is the supply, the coil may be fouled.
  • MarkBentfield
    MarkBentfield Member Posts: 2
    Turned out to be a failed Taco pump. The lack of flow caused the boiler to trip off on high temp. With a new pump the system is modulating and performing as intended. Thanks all for your comments.
    Mark B
  • kcopp
    kcopp Member Posts: 4,089
    that was easy....