Lennox ML193UHE furnace 9 red flashes: Pressure Switch Not Proven
Professional repair
What do 9 red LED flashes mean on a Lennox ML193UHE with ignition control 103217-03? 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.
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 →
A technician should check the inducer, vent, condensate drainage and pressure-proving circuit. The code does not prove the switch itself failed, and the switch must not be bypassed or adjusted.
Possible causes
- Inducer, venting or condensate problem affecting pressure proving 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 9 red LED flashes mean on a Lennox ML193UHE with ignition control 103217-03?
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.
How do I fix Lennox ML193UHE furnace 9 red flashes?
Book service and report the flash count and whether the furnace stopped before or after it began heating. Leave pressure hoses, switches and vent connections untouched. If the code changes to ten flashes, the control has entered pressure-switch Watchguard.
How much does it cost to fix Lennox ML193UHE furnace 9 red flashes?
Cost follows the diagnosis: an inducer, venting, drainage or switch problem each involves different parts and labor. A pressure-switch code alone does not justify replacing the switch.
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.