Lennox ML193UHE furnace 10 red flashes: Pressure Switch Watchguard
Professional repair
What do 10 red LED flashes mean on a Lennox ML193UHE with ignition control 103217-03? 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.
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 needs to find why pressure proving keeps dropping out, looking at the inducer, venting and condensate path. Do not bypass, adjust or jumper the pressure switch.
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 10 red LED flashes mean on a Lennox ML193UHE with ignition control 103217-03?
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.
How do I fix Lennox ML193UHE furnace 10 red flashes?
Arrange service instead of restarting the furnace. Note how many times you heard it start and stop before the code appeared. Leave the switch, hoses and venting alone; repeated openings need a cause identified before normal use.
How much does it cost to fix Lennox ML193UHE furnace 10 red flashes?
Expect diagnostic time to trace intermittent pressure loss, which can take longer than a fault that is present all the time. Parts depend on the finding.
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.