Lennox ML193UHE furnace 11 red flashes: Pressure Switch Closed
Professional repair
What do 11 red LED flashes mean on a Lennox ML193UHE with ignition control 103217-03? 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.
This condition involves the gas or combustion side. If you smell gas or a CO alarm sounds: leave, then call your gas utility. Diagnostic info here is reference — combustion repairs are for licensed technicians. All six emergency signs →
Testing the pressure switch and its control circuit is technician work. The switch must never be jumpered or bypassed to get the furnace running.
Possible causes
- Pressure switch or control-circuit wiring condition 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 do 11 red LED flashes mean on a Lennox ML193UHE with ignition control 103217-03?
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.
How do I fix Lennox ML193UHE furnace 11 red flashes?
Call for service and give the flash count. A technician checks whether the switch contacts or wiring are holding the circuit closed and corrects the cause. The furnace should not be forced to run while the switch reads closed early.
How much does it cost to fix Lennox ML193UHE furnace 11 red flashes?
Costs cover diagnosis of the switch and its wiring, plus any switch replacement the technician confirms is needed. A wiring correction is mostly labor.
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
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