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 G60UHV Service Manual

PROBLEM 5: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER
Condition
5.1
− Unit operates with a cooling and
continuous fan demand.
− 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 6: BURNERS LIGHT WITH A HEATING DEMAND BUT UNIT SHUTS DOWN
Condition
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
6.2
− Combustion air inducer energizes
with a heating demand.
− Burners light but fail to stay lit.
− After 5 tries the control diagnostics
flash the watchguard burners failed to
ignite code.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
ENERGIZES, IGNITOR IS ENERGIZED.
Possible Cause
5.1.1
Check that gas is being supplied to
the unit.
5.1.2
Miswiring of gas valve or loose con-
nections at multi−pin control amp
plugs or valve.
5.1.3
Defective gas valve or ignition con-
trol.
PREMATURELY
Possible Cause
6.1.1
Low pressure differential at the prove
switch.
6.2.1
Sensor or sense wire is improperly
installed.
6.2.2
Sensor or sense wire is broken.
6.2.3
Sensor or sensor wire is grounded to
the unit.
6.2.4
Control does not sense flame.
Page 61
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 exhaust vent.
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 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.