Lennox ML193UHE furnace 1 red flash: Reversed Polarity
Professional repair
What does 1 red LED flash mean on a Lennox ML193UHE with ignition control 103217-03? 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.
Before you touch anything: the six signs that mean stop troubleshooting and call a pro →
Polarity checks and wiring corrections involve live line-voltage circuits, so they belong to a licensed technician or electrician. Give them the flash count and when the code appears.
Possible causes
- Hot and neutral conductors reversed in the furnace supply wiring TECH
Parts for this code
No model-verified part number is listed here. Have the fault diagnosed and the correct part matched to your furnace before ordering.
Questions about this code
What does 1 red LED flash mean on a Lennox ML193UHE with ignition control 103217-03?
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.
How do I fix Lennox ML193UHE furnace 1 red flash?
Leave the wiring alone and book service. Note the flash count, whether the thermostat was calling for heat, and whether the furnace tried to start. A technician confirms polarity at the furnace and corrects the supply wiring before the furnace is returned to normal use.
How much does it cost to fix Lennox ML193UHE furnace 1 red flash?
Expect a diagnostic visit plus electrical labor. The bill depends on where the reversal is, at the furnace connection or further back in the house circuit.
Related symptoms
These symptoms can appear alongside this code. The link is an association, not a diagnosis, and code meanings vary by brand, model and control.
Applies to
ML193UHE
Different Lennox generations use different code maps. If your series isn't listed, don't assume this meaning — check your blower-door label.
Verified against Lennox ML193UHE Installation Instructions, p.39
Verified against Lennox ML193UHE Unit Information / Service Literature, p.9
Last verified 2026-10-07 · page updated 2026-10-07 · how we verify
Related Lennox furnace codes
These codes use the same lennox ml193uhe with ignition control 103217-03 system.