Lennox furnace error codes
This page covers the Lennox ML193UHE gas furnace when it has ignition control 103217-03. The board reports status with a red LED. Counted flash groups separated by a 3-second pause mean a fault. A slow 1-second on, 1-second off pattern or a continuous rapid flash is a normal state. Check both the full model number on the rating plate and the diagnostic label on the door before using this chart. A flash count tells you what the control observed. It does not by itself confirm which part has failed.
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How to read the red LED
Count the red flashes in one group, then wait for the 3-second pause before the group repeats. Each flash lasts about half a second. A slow, even blink (1 second on, 1 second off) means the furnace is idle, running the fan, or cooling. Continuous rapid flashing with no pause means a heat call is underway. It does not prove the burner is producing heat. A dark LED means no control power or a board fault. Note what you see without defeating the door switch.
What this chart covers
The chart lists all 15 live rows for control 103217-03: twelve numbered faults (1 to 5 and 7 to 13), the dark-LED fault state and two normal states. Code 6 is unused on this board. The same Lennox manual has a separate table for control 107163-01, including a solid-on state, and that table is not merged here. Documented models are ML193UH030XE36B, ML193UH045XE36B, ML193UH070XE36B, ML193UH090XE36C, ML193UH090XE48C, ML193UH110XE48C and ML193UH110XE60C. Code recall and clearing are service functions, not homeowner steps.
- Lennox ML193UHE with ignition control 103217-03: ML193UHE
ML193UHE control 103217-03 red LED code chart
| Code or flash pattern | Meaning | Model family | Details |
|---|---|---|---|
| Red LED: 1 flash, then 3-second pause | Reversed Polarity The ignition control has detected that the line-voltage supply is wired with reversed polarity. The control uses this code to report a power-wiring condition, not a failed component. | ML193UHE | View details |
| Red LED: 2 flashes, then 3-second pause | Improper Earth Ground The ignition control has detected an improper earth ground at the furnace. The code reports the electrical condition the board sees; it does not identify where in the circuit the ground is missing. | ML193UHE | View details |
| Red LED: 3 flashes, then 3-second pause | Ignition or Flame Failure During a heat demand, the burners either failed to ignite or the control lost the flame signal after ignition. The same three-flash code covers both events, so it does not tell you which one occurred. | ML193UHE | View details |
| Red LED: 4 flashes, then 3-second pause | Low Flame Signal The control is reading a weak flame signal. Lennox's table pairs this code with a flame-sensor check and does not list it as a lockout. | ML193UHE | View details |
| Red LED: 5 flashes, then 3-second pause | Ignition Watchguard The control reached its maximum number of ignition retries or recycles and entered Watchguard. Lennox service literature describes five total ignition trials followed by a 60-minute Watchguard period before the control tries again. | ML193UHE | View details |
| Red LED: 7 flashes, then 3-second pause | Limit Switch Open The primary or secondary limit switch has opened. When the primary limit opens, the gas valve shuts and the blower runs; the same code also marks Watchguard if a limit stays open longer than 3 minutes. | ML193UHE | View details |
| Red LED: 8 flashes, then 3-second pause | Rollout Switch Open The flame-rollout safety switch is open. The control closes the gas valve, and the switch requires a manual reset after a technician identifies and corrects the cause. | ML193UHE | View details |
| Red LED: 9 flashes, then 3-second pause | Pressure Switch Not Proven During a heat demand, the pressure switch either did not close or opened after closing. It is part of the pressure-proving circuit tied to the combustion-air inducer and venting. | ML193UHE | View details |
| Red LED: 10 flashes, then 3-second pause | Pressure Switch Watchguard The pressure switch opened five times during a single heat demand, so the control entered Watchguard. It reflects repeated loss of pressure proving rather than one isolated event. | ML193UHE | View details |
| Red LED: 11 flashes, then 3-second pause | Pressure Switch Closed The pressure switch was already closed before the combustion-air inducer started. The control expects it open at that point, so the reading points to a switch or control-circuit condition. | ML193UHE | View details |
| Red LED: 12 flashes, then 3-second pause | Unexpected Flame The control sensed flame while the gas valve was not energized. Flame should not be present then, so this is a safety condition, not a routine fault. | ML193UHE | View details |
| Red LED: 13 flashes, then 3-second pause | Low Line Voltage The ignition control is reporting low line voltage on the furnace's power supply. The code identifies a supply condition, not a specific failed part in the furnace. | ML193UHE | View details |
| Red LED off (dark, no flashing) | No Power or Board Fault A dark LED means the control has no power or has detected a board fault. It does not say which of the two applies. | ML193UHE | View details |
| Red LED slow flash: 1 second on, 1 second off | Normal Idle Status This is a normal status. The control is idle with no heat demand, running the fan continuously, or operating in cooling mode. | ML193UHE | View details |
| Red LED continuous rapid flash, no pause | Heat Call in Progress The control is reporting an active heat call and burner operation sequence. Lennox's 103217-03 table does not give exact on/off timing for this flash. | ML193UHE | View details |
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