Gibson Furnaces Error Codes

1 FLASH

Status LED flashes once repeatedly, furnace will not start heating cycle

Ignition Failure / No Flame Detected

2 FLASHES

Status LED flashes twice repeatedly, furnace starts but shuts down shortly after ignition

Pressure Switch Stuck Closed

3 FLASHES

Status LED flashes three times, inducer runs but burners do not light

Pressure Switch Stuck Open / Venting Problem

4 FLASHES

Status LED flashes four times, furnace shuts down shortly after ignition, may retry several times

Open High Limit Switch / Overtemperature

5 FLASHES

Status LED flashes five times, furnace will not start heating cycle

Flame Sensed With Gas Valve Off (False Flame Signal)

6 FLASHES

Status LED flashes six times, furnace locks out and will not heat

Pressure Switch Cycle Fault / Intermittent Venting Issue

7 FLASHES

Status LED flashes seven times, furnace attempts ignition but shuts down quickly

Flame Loss During Run

8 FLASHES

Status LED flashes eight times, furnace will not start heating cycle

Ignitor Circuit Fault

9 FLASHES

Status LED flashes nine times, blower may run continuously without heat

Reversed Line Polarity or Grounding Issue

BLOWER FAULT (DISPLAY)

Display indicates blower fault, no airflow or intermittent airflow during heat call

Blower Motor or ECM Module Failure

LIMIT OPEN (DISPLAY)

Furnace display or diagnostic label indicates limit open, blower runs but burners off

Open High Limit or Auxiliary Limit Switch

LOCKOUT (DISPLAY)

Control indicates ignition lockout, furnace will not attempt to start until power is cycled

Ignition Lockout After Repeated Failed Attempts

NO LED

No LED lights, furnace completely dead, no blower or inducer operation

No Power to Furnace / Failed Transformer or Control Board

PRESSURE SWITCH ERROR (DISPLAY)

Display shows pressure switch error, furnace will not ignite

Pressure Switch or Venting Fault

STEADY ON

Status LED solid on with no flashing, furnace not responding to thermostat

Normal Power On / No Call for Heat or Board Locked

Symptom

Blower runs continuously even when thermostat is not calling for heat or fan

Continuous Fan Operation

Symptom

Furnace blower starts and stops repeatedly without burner ignition

Fan-Only Cycling / Control Logic Fault

Symptom

Furnace cabinet sweats or shows condensation on the outside

Condensation / Humidity Issue

Symptom

Furnace causes frequent tripping of circuit breaker

Electrical Overload or Short Circuit

Symptom

Furnace cycles off on very cold days but runs normally in mild weather

Marginal Venting or Combustion Air Problem

Symptom

Furnace ignites but blower comes on very late, blowing very hot air and sometimes tripping limit

Blower On-Delay Control Problem

Symptom

Furnace is very noisy during operation (rattling, squealing, or grinding)

Mechanical Noise / Vibration

Symptom

Furnace makes loud booming or banging noise at startup

Delayed Ignition / Burner Light-Off Problem

Symptom

Furnace produces a strong burning or electrical smell when running

Overheating Components or Electrical Overload

Symptom

Furnace runs but carbon monoxide detector alarms when it operates

Combustion / Venting Hazard

Symptom

Furnace runs but does not produce enough heat; home never reaches set temperature

Underfiring or Insufficient Heat Output

Symptom

Furnace runs but some rooms are too hot while others are too cold

Air Distribution / Duct Imbalance

Symptom

Furnace short cycles, turning on and off frequently without long run times

Short Cycling

Symptom

Furnace shuts off and on when the blower speed changes or when another large appliance starts

Voltage Drop / Electrical Interference

Symptom

Furnace starts then shuts off within a few seconds, repeating several times

Flame Rollout or Safety Trip

Symptom

Furnace will not start at all, but power and LED are present

No Call for Heat / Thermostat Circuit Fault

Symptom

Thermostat goes blank when furnace tries to start

Low-Voltage Short or Transformer Overload

Symptom

Water leaking around base of furnace or inside cabinet

Condensate Leak