33
Problem
LED Code
Fault/Cause
Solution
■
Furnace fails to operate
■
Integrated control module
diagnostic LED provides
no signal
None
■
No 115-volt power to furnace, or no
24-volt power to integrated control
module.
■
Blown fuse or circuit breaker.
■
Internal fault in Integrated control
module.
■
Manual disconnect switch off, door
switch open or 24-volt wires
improperly connected or loose.
■
Verify that there is 115-volt power to the
furnace and 24-volt power to integrated
control module
■
Replace fuse or circuit breaker.
■
Check integrated control module fuse
(3A). Replace if necessary.
■
Check for possible shorts in 115- and
24-volt circuits. Repair as necessary.
■
Replace bad integrated control module.
■
LED is steady On.
Continuous
On—not
flashing
■
Normal
■
None
■
Furnace fails to operate.
■
Integrated control module
diagnostic LED is flashing
1 flash.
1 flash
■
Furnace lockout due to an excessive
number of ignition “retries” (3 total).
■
Auxiliary limit switch open.
■
Failure to establish flame. Cause may
be no gas to burners, bad igniter or
igniter alignment, improper orifices or
coated/oxidized or improperly
connected flame sensor.
■
Loss of flame after establishment.
Cause may be interrupted gas supply,
lazy burner flames (improper gas
pressure or restriction in flue) or
improper induced draft blower
performance.
■
Insufficient conditioned air over the
heat exchanger. Blocked filters,
restrictive ductwork, improper
circulator blower speed or failed
circulator blower.
■
Locate and correct gas interruption.
■
Replace or realign igniter. Igniter is fragile;
handle gently.
■
Check flame sense signal. Sand sensor
with emery cloth if coated and/or
oxidized.
■
Check flue piping for blockage, proper
length, elbows and termination. See
“Vent/Flue Pipe.”
■
Verify proper induced draft blower
performance.
■
Check circulator blower speed and
performance. Correct speed or replace
blower, if necessary.
■
Furnace fails to operate.
■
Integrated control module
diagnostic LED is flashing
2 flashes.
2 flashes
■
Pressure switch circuit is closed.
■
Induced draft blower is not operating.
■
Induced draft blower pressure switch
contacts sticking.
■
Shorts in pressure switch circuit.
■
Replace induced draft blower pressure
switch.
■
Repair short.
■
Induced draft blower runs
continuously with no
further furnace operation.
■
Integrated control module
diagnostic LED is flashing
3 flashes.
3 flashes
■
Pressure switch circuit not closed.
■
Induced draft blower is operating.
■
Pressure switch hose blocked, pinched
or connected improperly.
■
Blocked flue or weak induced draft
blower.
■
Incorrect pressure switch setpoint or
malfunctioning switch contacts.
■
Loose or improperly connected wiring.
■
Inspect pressure switch hose. Repair, if
necessary.
■
Inspect flue for blockage, proper length,
elbows and termination. Correct as
necessary.
■
Correct pressure switch setpoint or
contact motion.
■
Tighten or correct wiring connection.
■
Circulator blower runs
continuously. No furnace
operation.
■
Integrated control module
diagnostic LED is flashing
4 flashes.
4 flashes
■
Primary limit circuit is open.
■
Insufficient conditioned air over the
heat exchanger. Blocked filters,
restrictive ductwork, improper
circulator blower speed or failed
circulator blower.
■
Faulty primary limit switch.
■
Loose or improperly connected wiring.
■
Check primary limit switch. Replace, if
necessary.
■
Check filters and ductwork for blockage.
Clean filters or remove obstruction.
■
Check circulator blower speed and
performance. Correct speed or replace
blower if necessary.
■
Tighten or correct wiring connection.