GC9C80 Service Manual


Symptom LED Status Fault Description Corrective Actions
Normal operation

Normal operation None
Locate and correct gas interruption
Replace or realign igniter
Check flame sense signal, clean sensor if coated or
oxidized
Check flue piping for blockage, proper length, elbows, and
termination
Verify proper induced draft blower performance
Low stage pressure switch circuit is closed at
start of heating cycle
Low stage pressure switch contacts sticking
Short in pressure switch circuit wiring
Inspect flue for blockage, proper length, elbows, and
termination
Check induced draft blower performance, correct as
necessary
Check pressure switch operation, replace as needed
Tighten or correct wiring connection
Primary limit circuit is open
Check filters and ductwork for blockage Clean filters or
remove obstruction
Insufficient conditioned air over the heat
exchanger
Check circulator blower speed and performance
Blocked filters, restrictive ductwork, improper
circulator blower speed, or failed circulator
blower motor
Correct speed or replace blower motor if necessary
Loose or improperly connected wiring in high
limit circuit
Tighten or correct wiring connection
Flame sensed with no call for heat Correct short at flame sensor or in flame sensor wiring
Short to ground in flame sense circuit
Lingering burner flame Slow closing gas
valve
Open fuse Replace fuse
Short in low voltage wiring Locate and correct short in low voltage wiring
Induced draft blower and
circulator blower runs
continuously
No furnace operation

Check for lingering or lazy flame Verify proper operation of
gas valve
No furnace operation

TROUBLESHOOTING CHART
Induced draft blower runs
continuously with no furnace
operation

Inspect pressure switch hose, repair/replace if necessary
Low stage pressure switch circuit is not
closed
Pressure switch hose blocked pinched, or
connected improperly
Blocked flue pipe, or weak induced draft
blower
Incorrect pressure switch set point or
malfunctioning switch contacts
Loose or improperly connected wiring
Replace low stage pressure switch Repair short in wiring
Circulator blower runs
continuously
No furnace operation

Furnace fails to operate

Furnace lockout due to an excessive number
of ignition “retries” (3 total)
Failure to establish flame
Loss of flame after establishment
Furnace fails to operate


• Press either the Left or Right switch until L 6 F is displayed.
• Press the center switch to view stored faults.
• Press and hold the center switch for 5 to 30 seconds.
• All stored faults will be erased, and the display will ash - - - three times and return to L 6 F.
TROUBLESHOOTING
36