1 flash
System lockout (retries exceeded)
This code typically points to
- Flame not sensed during ignition trials leading to lockout after repeated retries
Next checks to confirm
- Check ignition sequence
- Verify flame establishment
- Inspect gas interruption, igniter, flame sensor, pressure-switch proving, and induced-draft performance per applicable service manual
Escalation
Three ignition tries total, then lockout
Reset behavior
Reset by turning thermostat off for more than 5 seconds and less than 20 seconds and back on, or by turning furnace power off for a minimum of 5 seconds; automatic reset after one hour.
Urgent
Fix now