6
Flame not sensed during trial for ignition, or flame signal lost during blower-on delay
This code typically points to
- Gas valve off
- Manual shutoff valve
- Missing green/yellow ground wire to furnace sheet metal
- Grounded flame sensor
- Oxide buildup on flame sensor
- Inadequate flame carryover/rough ignition
- Defective HSI
- Low inlet gas pressure
Next checks to confirm
- OEM sequence: component test for igniter
- Verify 115V to igniter
- Verify 24V to gas valve
- Observe burner ignition/stability
- Measure flame current
Escalation
If four attempts fail, progresses to 6+1.
Reset behavior
Repeats ignition sequence 3 more times before 6+1 lockout.
Urgent
Fix now