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Munchkin 80M throwing F9 and f10 codes

Beginning two weeks ago the boiler faulted with an F9, flame loss code. the flame rod was cleaned and restarted normally and operated for two more days, then F9 or F10 code. Boiler wouldn't relight and was left for another visit a week later. All related to me by another technician.
At the time of my first visit, restarted normally, and recovered ignition when the flame rod lead had been removed in order to measure uA. The microamperage reading initally was 0.7-0.8 (below spec) and then slowly climbed to 3.0 or so. During the same visit, the condensate drain was supported to eliminate a sag at the back of the unit and the air intake pipe was secured in place. Unit ran normally for an afternoon and failed in the evening with an F10 code.
I shall replace the flame sensor ASAP. Any knowledge if a Lochinvar model of similar design will work?
After this, what shall I look towards to the nature of this malfunction?
The first Munchkin Ive ever had my hands on.


  • Alan (California Radiant) ForbesAlan (California Radiant) Forbes Member Posts: 2,266
    edited October 2019
    Check these:

    With all the old Munchkins out there, I always check to see if it has the current 926 circuit board that has a few improvements. The old boards can sometimes throw out erroneous error codes - typically "F12".

    The new 926 board has a black transformer. The old 925 boards have a red transformer. They are fairly easy to replace.
    Often wrong, never in doubt.

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  • JUGHNEJUGHNE Member Posts: 6,783
    Has this been opened for cleaning?
    Early units had drain problems and the HEX would fill with cond water. This would get the front insulation wall wet and tend to short out the FS rod.
    The factory tech svc recommended trimming the material around the entry point of the FS so no contact with insulation wall.
  • BoilershepherdBoilershepherd Member Posts: 9
    I have not opened this unit yet. But I have been thinking to clean the burner too. It never fails to surprise me how much dust blows off the burner socks of the Knights Ive encountered. Thank you each for the considerations.
  • HomerJSmithHomerJSmith Member Posts: 878
    edited October 2019
    Clean the heat exchanger and be sure and tighten the screws holding the burner tube in place, really tight, also, replace the burner tube gasket. A loose burner tube will give you an F09.

    F10--On the rear of the gas valve is a brass nipple (vent) and sometimes the boiler will shift and that vent will touch the rear of the cabinet. Drill a 3/8" hole in the black plastic cabinet where the vent is. Just drill thru the inner wall and not all the way to the outside. The vent should be surrounded by the hole.

    The microamps on start up should be above 2.5 and rapidly increase to + 4.0 uamps. Clean the rods with wet and dry sandpaper. The width of the gap, if spark ignition, should be about the thickness of two quarters placed together, about 1/4".

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