Lennox
G60UHX Series, Service Manual

Page: 38 / 40

Page 38
PROBLEM 5: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER
ENERGIZES, IGNITOR IS ENERGIZED.
Condition Possible Cause Corrective Action/Comments
5.1
− Unit operates with a cooling and
continuous fan demand.
Combustion air inducer energizes
5.1.1
Check that gas is being supplied to
the unit.
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.
− Combustion air inducer energizes
with Heating demand.
− Ignitor is energized but unit fails to
light.
5.1.2
Miswiring of gas valve or loose con-
nections at multi−pin control amp
plugs or valve.
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
5.1.3
Defective gas valve or ignition con-
trol.
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.
PROBLEM 6: BURNERS LIGHT WITH A HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY
Condition Possible Cause Corrective Action/Comments
6.1
− Burners fire with a heating demand.
− Burners light but unit shuts off prior
to satisfying T−stat demand.
− Diagnostic lights flash the pressure
switch code.
LED#1−Off
LED#2−Slow Flash
6.1.1
Low pressure differential at the pres-
sure switch.
ACTION 1 − Check for restricted exhaust vent.
Remove all blockage.
ACTION 2: Check for proper vent sizing. See
installation instructions.
6.2
− Combustion air inducer energizes
with a heating demand.
B li ht b t f il t t lit
6.2.1
Sensor or sense wire is improperly
installed.
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.
− Burners light but fail to stay lit.
− After 5 tries the control diagnostics
flash the watchguard burners failed to
ignite code.
6.2.2
Sensor or sense wire is broken.
ACTION 1 − Check for a broken sensor.
ACTION 2 − Test continuity across the sense
wire. If wire or sensor are damaged replace the
component.
ignite code.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
6.2.3
Sensor or sensor wire is grounded to
the unit.
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.
6.2.4
Control does not sense flame.
ACTION 1 − Check the microamp signal from
the burner flame. If the microamp signal is be-
low 0.23 microamps, 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.
ACTION 3 − Check that there is proper ground
to burner box. Repair as necessary.