Pressure Switch - Lennox G24M SERIES Unit Information

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 blower ener- Combustion air blower ener
gizes 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 de-
mand.
-- Burners light but unit shuts off
prior to satisfying T--stat demand.
-- Diagnostic lights flash the pres-
sure switch code.
LED#1--Off
LED#2--Slow Flash
6.2
-- Combustion air blower energizes
with a heating demand.
-- Burners light but fail to stay lit. B li ht b t f il t
-- After 5 tries the control diagnos-
tics flash the watchguard burners
failed to ignite code. failed to ignite code.
LED#1--Alternating Slow Flash
LED#2--Alternating Slow Flash
ENERGIZES, IGNITOR IS ENERGIZED. (CONT.)
Possible Cause
Check that gas is being supplied to
Miswiring of gas valve or loose
connections at multi--pin control
amp plugs or valve.
Malfunctioning gas valve or igni-
PREMATURELY
Possible Cause
Low pressure differential at the

pressure switch.

Sensor or sense wire is improperly
t lit
Sensor or sense wire is broken.
Sensor or sensor wire is grounded
Control does not sense flame.
5.1.1
the unit.
5.1.2
5.1.3
tion control.
6.1.1
6.2.1
installed.
6.2.2
6.2.3
to the unit.
6.2.4
3DJH 
Corrective Action/Comments
ACTION 1 - - Check line pressure at the gas
valve. Pressure should not exceed 13” WC for
both natural and propane. Line pressure
should read a minimum 4.5” WC for natural
and 8.0”WC for propane.
ACTION 1 - - Check for correct wiring and
loose connections. Correct wiring and/or re-
place any loose connections.
ACTION 1 - - Check that 24V is supplied to the
gas valve approximately 35 seconds after
heat demand is initiated.
ACTION 2 - - Replace the valve if 24V is sup-
plied but valve does not open (check for ex-
cessive gas line pressure before replacing
gas valve).
ACTION 3 - - Replace the control board if 24V
is not supplied to valve.
Corrective Action/Comments
ACTION 1 - - Check for restricted vent inlet or
exhaust. Remove all blockage.
ACTION 2: Check for proper vent sizing. See
installation instructions.
ACTION 1 - - Check that sensor is properly
located (page 10) and that the sense wire is
properly attached 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 cir-
cuit.
ACTION 1 - - Check the microamp signal
from the burner flame. If the microamp sig-
nal is below 0.70 microamps, check the
sense rod for proper location or contamina-
tion.
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 PA-
PER WILL CONTRIBUTE TO THE CONTAMI-
NATION PROBLEM. NOTE: Do not attempt
to bend sense rod.