Unit Fails To Fire In The Heating Mode, Combustion Air Blower Energizes, Ignitor Is Energized; Burners Light With A Heating Demand But Unit Shuts Down Prematurely - Lennox G61MPV Service Manual

PROBLEM 4: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER
Condition
4.1
− Unit operates with a cooling and
continuous fan demand.
− Combustion air inducer energizes Combustion air inducer energizes
with Heating demand.
− Ignitor is energized but unit fails to
light.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
PROBLEM 5: BURNERS LIGHT WITH A HEATING DEMAND BUT UNIT SHUTS DOWN
Condition
5.1 5.1
− Burners fire with a heating demand.
− Burners light but unit shuts off prior
to satisfying T−stat demand.
− Diagnostic lights flash the pressure − Diagnostic lights flash the pressure
switch code.
LED#1−Off LED#1 Off
LED#2−Slow Flash
5.2
− Combustion air inducer energizes
with a heating demand.
− Burners light but fail to stay lit. B rners light b t fail to sta lit
− After 5 tries the control diagnostics
flash the watchguard burners failed to
ignite code. ignite code.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
ENERGIZES, IGNITOR IS ENERGIZED.
Possible Cause
4.1.1
Check that gas is being supplied to
the unit.
4.1.2
Miswiring of gas valve or loose-
connections at multi−pin control amp
plugs or valve.
4.1.3
Defective gas valve or ignition
control.
PREMATURELY
Possible Cause
5.1.1
Low pressure differential at the prove
switch.
5.1.2
Wrong concentric vent kit used for
terminating the unit.
5.1.3
Condensate drain line is not draining
properly.
5.1.4
Low pressure differential at the prove
switch.
5.2.1
Sensor or sense wire is improperly
installed.
5.2.2
Sensor or sense wire is broken.
5.2.3
Sensor or sensor wire is grounded to
the unit.
5.2.4
Control does not sense flame.
Page 94
Corrective Action/Comments
ACTION 1 − Check line pressure at the gas valve.
Pressure should not exceed 13" WC for both nat-
ural and propane. Line pressure should read a
minimum 4.5" WC for natural and 8.0"WC for pro-
pane.
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
ACTION 1 − Check that 24V is supplied to the gas
valve approximately 35 seconds after heat de-
mand is initiated.
ACTION 2 − Replace the valve if 24V is supplied
but valve does not open.
ACTION 3 − Replace the control board if 24V is
not supplied to valve.
Corrective Action/Comments
ACTION 1 − Check for restricted intake and ex-
haust vent. Remove all blockage.
ACTION 2: Check for proper vent sizing. See
installation instructions.
ACTION 1 − Check vent termination kit installed.
See Placement and Installation section.
ACTION 1 − Check condensate line for proper
vent slope, and any blockage. Condensate
should flow freely during operation of furnace.
Repair or replace any improperly installed con-
densate lines.
ACTION 1 − Check for restricted intake and ex-
haust. Remove all blockage.
ACTION 2: Check for proper vent sizing. See
installation instructions.
ACTION 1 − Check that sensor is properly lo-
cated and that the sense wire is properly at-
tached to both the sensor and the control.
ACTION 1 − Check for a broken sensor.
ACTION 2 − Test continuity across the sense
wire. If wire or sensor are damaged replace the
component.
ACTION 1 − Check for resistance between the
sensor rod and the unit ground.
ACTION 2 − Check for resistance between the
sensor wire and the unit ground.
ACTION 3 − Correct any shorts found in circuit.
ACTION 1 − Check the microamp signal from
the burner flame. If the microamp signal is be-
low normal, check the sense rod for proper
location or contamination.
ACTION 2 − Replace, clean, or relocate flame
sense rod. If rod is to be cleaned, use steel
wool or replace sensor. DO NOT CLEAN ROD
WITH SAND PAPER. SAND PAPER WILL
CONTRIBUTE TO THE CONTAMINATION
PROBLEM. NOTE: Do not attempt to bend
sense rod.