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Explanation: The bL81 can be triggered if the flue gas plug has gotten wet and then dried out. (MCBA sees resistance when wet and
then sees no resistance when dry) This tricks the MCBA into thinking that a flue gas sensor was installed and then removed in which
the bL 81 is triggered. Moisture can come from a clog, broken or dry condensate trap. Moisture can be from a leaking concentric
vent pipe or from driving rain during extreme weather.
Methods to rectify:
A. ORDER AND INSTALL A FLUE GAS SENSOR (This may not be possible in cold weather when boiler must operate
immediately, if shipping the part is required.
B. CHANGE PARA 80 TO 20 AND INSTALL LOW VOLTAGE JUMPER ON FLUE GAS PLUG - (plug located on upper left hand side
of the heat exchanger in the harness) (PARA 20 setting causes the MCBA to look for an open/ close circuit and ignores any
variable resistance values like moisture or a thermistor.
C. INSTALL A 10K OHM RESISTOR ACROSS FLUE GAS TERMINALS. This will make the MCBA think that the flue gas is at a safe
temperature level (90 F)
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