Lennox ML193UHE furnace 4 red flashes: Low Flame Signal
Professional repair
What do 4 red LED flashes mean on a Lennox ML193UHE with ignition control 103217-03? 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.
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 →
Measuring flame signal and servicing the flame sensor belong to a technician. Lennox supplies no homeowner cleaning or removal procedure, so leave the sensor in place.
Possible causes
- Flame sensor condition, which Lennox directs technicians to check 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 4 red LED flashes mean on a Lennox ML193UHE with ignition control 103217-03?
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.
How do I fix Lennox ML193UHE furnace 4 red flashes?
If the furnace is still heating, note the code and arrange a service visit. The technician measures the flame signal, inspects the sensor and its wiring, and decides whether the sensor needs service or replacement.
How much does it cost to fix Lennox ML193UHE furnace 4 red flashes?
The bill covers diagnosis and any sensor service. Replacement, if needed, adds a part and fitting time; the signal measurement decides which applies.
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.