Lennox EL280UHE Series Service Literature page 41

CONTINUED
FIRST-STAGE (LOW FIRE) PRESSURE
1
SWITCH CLOSED WITHIN 2.5 MINUTES?
YES
15-SECOND COMBUSTION AIR INDUCER
PRE-PURGE INITIATED BY CLOSED FIRST-STAGE
PRESSURE SWITCH (or 15 SECOND
INTER-PURGE PERIOD.)
1
STATUS LED -- HEARTBEAT.
IGNITOR WARM-UP (20 SECONDS)
STATUS LED -- HEARTBEAT.
YES
IS IGNITOR INTACT AND CONNECTED?
YES
2
AT END OF IGNITOR 20 SECOND WARM UP
PERIOD, 4-SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS, IGNITOR ENERGIZED DURING
4-SECOND TRIAL UNTIL FLAME SENSED.
YES
4-SECOND FLAME STABILIZATION PERIOD.
FLAME RECTIFICATION CURRENT CHECK
CAN FLAME BE PROVEN WITHIN 4
SECONDS AFTER GAS VALVE OPENS?
( 0.19 microamps)
FLAME PRESENT?
YES
CONTINUED ON NEXT PAGE
If the furnace is operating on continuous fan mode (terminals "R" and "G" are energized), the combustion
1
air inducer will energize on high speed, the gas valve will energize on second-stage heat and the furnace
will operate on high fire. Furnace will stay on high fire 60 seconds then switch to low fire.
2
If combustion air inducer is operating on high speed and gas valve is energized on second-
stage heat, 20 seconds after flame is sensed furnace will switch to low fire.
HEATING SEQUENCE OF OPERATION
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF. INDOOR BLOWER OFF. UNIT WILL RETRY
NO
COMBUSTION AIR INDUCER
ENERGIZED ON HIGH SPEED
COMBUSTION AIR INDUCER OFF, IGNITOR OFF.
NO
COMBUSTION AIR INDUCER OFF, IGNITOR OFF.
SIGNAL HOLDS UNTIL VOLTAGE RISES ABOVE 95
NO
GAS VALVE OFF. COMBUSTION AIR
INDUCER ON. INDOOR BLOWER OFF.
FLAME FOR FIVE CONSECUTIVE TRIES
DURING A SINGLE HEAT DEMAND?
WATCHGUARD MODE. GAS VALVE OFF,
IS 60-MINUTE RESET PERIOD COMPLETE?
NO
HAS CONTROL RESET IGNITION SEQUENCE
STATUS ERROR CODE 4 + 3.
Page 41
THERMOSTAT CALLS FOR HEAT
STATUS LED - HEARTBEAT.
(Refer to box A on previous page)
AFTER 5-MINUTE WAIT PERIOD.
STATUS ERROR CODE 2 + 3.
LOW AND HIGH
PRESSURE SWITCH
CLOSED WITHIN 30
SIGNAL HOLDS UNTIL IGNITOR IS REPLACED
OR RECONNECTED.
STATUS ERROR CODE 4 + 7.
IS VOLTAGE ABOVE 90 VOLTS?
NO
VOLTS. STATUS ERROR CODE 4 + 8.
STATUS LED -- HEARTBEAT.
HAS CONTROL FAILED TO SENSE
YES
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF.
STATUS ERROR CODE 4 + 1.
YES
FOUR (4) TIMES?
WATCHGUARD MODE.
NO
YES
SECONDS
YES
NO
YES
NO