Troubleshooting - Lennox SL280UHNV Installation Instructions Manual

Troubleshooting: Heating Sequence of Operation
CALL FOR FIRST-STAGE HEAT
1
CALL FOR
1ST STAGE HEAT
(LOW FIRE)
HIGH
LIMIT SWITCH
CLOSED?
YES
ROLLOUT
CIRCUITS
CLOSED?
YES
LOW
PRESSURE
SWITCH
OPEN?
YES
INDUCER ON
LOW SPEED
LOW
PRESSURE SWITCH
CLOSED WITHIN 120
SECONDS?
YES
PRE−PURGE
(15 SECONDS)
H.S.I. ON
(20 SECONDS)
1ST STAGE GAS
VALVE ENERGIZED
IGNITION TRIAL
BEGINS (H.S.I. ON)
FLAME
SENSED WITHIN
4 SECONDS?
YES
H.S.I. OFF
INDOOR
BLOWER ON 30 SEC.
(LOW HEAT SPEED)
2
CALL FOR HEAT SATISFIED
INDOOR BLOWER OFF AFTER
HEAT FAN OFF DELAY
(LOW HEAT SPEED)
ERROR
INDOOR
NO
CODE
BLOWER
FLASHES
ON(LOW HEAT
SPEED)
INDUCER ON
(HIGH SPEED)
DE−ENERGIZE
NO
GAS VALVE
INDOOR BLOWER
ON (LOW HEAT
ERROR CODE
FLASHES (AFTER
NO
5 SECONDS)
LOW PRESSURE
SWITCH OPENS
HIGH
PRESSURE
SWITCH
OPEN
NO
BEFORE
INDUCER WAS
TURNED ON?
3
HEAT FAN ON DELAY
TIMER STARTED
GAS VALVE
DE−ENERGIZED
NO
H.S.I. OFF
1
WATCHGUARD LOCKOUT AUTOMATICALLY RESETS AFTER ONE HOUR
2 HARD LOCKOUT REQUIRES THERMOSTAT RESET OR CYCLING OF POWER TO RESET THE LOCKOUT.
3 IN CASE HIGH SPEED INDUCER IS RUNNING AT THE TIME THE GAS VALVE GETS ENERGIZED,
2ND STAGE GAS VALVE IS ENERGIZED INSTEAD OF 1ST STAGE. 20 SECONDS AFTER FLAME
IS SENSED, INDUCER SWITCHES TO LOW SPEED, AND GAS VALVE SWITCHES TO 1ST STAGE.
NO
YES
LIMIT
SWITCH
NO
CLOSED WITHIN 3
MINUTES?
ROLLOUT
ERROR
CODE
FLASHES
SPEED)
NO
LOW & HIGH
INDUCER TO
PRESSURE SWITCH
HIGH SPEED−
YES
CLOSED WITHIN 30
ERROR CODE
SECONDS?
FLASHES
NO
INTERPURGE
(15 SECONDS)
NO
5TH
POSTPURGE
UNSUCCESSFUL
YES
(5 SECONDS)
TRIAL?
Page 53
INDOOR
BLOWER OFF
WATCHGUARD −
AFTER HEAT FAN
ERROR CODE
OFF DELAY (LOW
FLASHES
HEAT SPEED)
CIRCUIT
CLOSES
YES
INDUCER OFF
AFTER POST
PURGE
INDOOR BLOWER
OFF AFTER HEAT
OFF DELAY
HARD LOCKOUT −
ERROR CODE
2
FLASHES
NO
YES
YES
INDUCER OFF−
WAIT
5 MINUTES
OFF AFTER
ERROR CODE
FLASHES
OFF DELAY
WATCHGUARD −
INDUCER
ERROR CODE
OFF
1
FLASHES
1
NO
CALL
FOR HEAT
ENDS?
YES
INDOOR INDOOR
BLOWER BLOWER
ON? ON?
NO
YES
INDOOR
BLOWER
HEAT FAN
1