Lennox G61MPV Service Manual page 104

PROBLEM 5: UNIT FIRES ON LOW FIRE, FAILS TO GO TO HIGH FIRE OPERATION
Flash Code
LED X + Y
5.1
− Unit light s normally during low fire
− Call for high fire inducer switches to
high fire for 10 seconds then back to
low fire.
− Diagnostic lights flash the high
pressure switch failure to close.
LED 2 + 5
Possible Cause
5.1.1
Prove switch does not close due to
obstruction in vent pipe.
5.1.2
Prove switch does not close due to
incorrect routing of the prove switch
line.
5.1.3
Prove switch does not close due to
obstructions in the prove switch line.
5.1.4
Prove switch line damaged
5.1.5
Condensate in prove switch line.
5.1.6
Prove switch does not close due to a
low differential prove across the
prove switch.
5.1.7
Wrong prove switch installed in the
unit, or prove switch is out of calibra-
tion.
5.1.8
Miswiring of furnace or improper con-
nections at prove switch.
5.1.9
Prove switch failure.
Page 104
Corrective Action/Comments
ACTION 1 − Check for restricted vent. Remove all
blockage.
ACTION 2: Check for proper vent sizing. See
installation instructions.
ACTION 1 − Check that the prove switch line is
correctly routed. Correctly route prove switch
line.
ACTION 1 − Remove any obstructions from the
the prove switch line and/or taps.
ACTION 1 − Check prove switch line for leaks.
Replace broken line if required.
ACTION 1 − Check prove switch line for conden-
sate. Remove condensate from line.
ACTION 1 − Check the differential pressure
across the prove switch. This pressure should
exceed the set point listed on the switch.
ACTION 2 − Check for restricted inlet vent. Re-
move all blockage.
ACTION 3 − Check for proper vent sizing and
run length. See installation instructions.
ACTION 1 − Check that the correct prove switch
is installed in the unit. Replace prove switch if
necessary.
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
ACTION 1 − If all the above modes of failure have
been checked, the prove switch may have failed.
Replace prove switch and determine if unit will
operate.