Lennox LED Blink Codes

No diagnostic fault has been recorded. System is normal.

1. No action needed

Maximum ignition retries exceeded. Furnace in lockout.

• Repeated ignition failure
• Gas supply issue
• Flame sensor fault

1. Power cycle to reset
2. Check gas supply
3. Clean flame sensor
4. Test igniter

Pressure switch did not close or opened during operation.

• Blocked flue or intake
• Failed pressure switch
• Inducer motor failure
• Hose issue

1. Inspect flue and intake pipes
2. Check pressure hose for cracks
3. Test pressure switch
4. Measure inducer motor amps

High temperature limit switch has tripped.

• Dirty air filter
• Restricted airflow
• Blower motor issue
• Oversized gas rate

1. Replace air filter
2. Check return and supply vents
3. Test blower motor
4. Check gas pressure

Control board sees flame when gas valve is off.

• Gas valve leaking
• Flame circuit short
• Board malfunction

1. SAFETY: Turn off gas supply
2. Test gas valve
3. Inspect flame sensor circuit

24V control circuit interruption detected.

• Power flicker
• Loose wire connection
• Weak transformer

1. Check transformer output
2. Tighten all wire connections
3. Inspect thermostat wiring

Igniter did not reach ignition temperature in expected time.

• Weak igniter
• Low voltage to igniter
• Board igniter output fault

1. Test igniter resistance
2. Check line voltage to board
3. Test igniter output from board

Flame was established but lost during the heating cycle.

• Dirty flame sensor
• Intermittent gas supply
• Weak flame signal
• Grounding issue

1. Clean flame sensor
2. Check gas pressure
3. Test flame signal (should be 2+ microamps)
4. Verify furnace ground