Lennox Furnace Error Code LED On

LED On on a Lennox furnace with the R7184B burner control means the cad cell flame sensor is detecting light or an actual flame at the burner. During an active heating cycle this is a normal indication of successful ignition. If it appears when the furnace should be off, it signals a problem such as extraneous light reaching the cad cell, a burner that is not shutting down, or a faulty sensor.

Resetting the burner control may temporarily clear a lockout caused by this condition, but if the underlying cause is not addressed, the condition will return. Resetting without diagnosis is not recommended, especially if the burner is suspected of running when it should not be. The root cause, whether it is a light leak, a contaminated cad cell, or a fuel system problem, must be identified and corrected first.

If the fix is simply closing an access panel or cleaning the cad cell, there may be little to no parts cost, though a service call typically runs between $80 and $150. Replacing a cad cell is generally an inexpensive repair, with parts usually in the $15 to $40 range plus labor. If the problem involves a faulty oil valve, burner control, or other larger component, total repair costs can range from $200 to $600 or more depending on parts and labor rates in your area.

It can indicate a safety concern if the burner is running when it should not be, or if the oil valve is failing to close properly. In those cases, the furnace should be shut off at the power switch and inspected by a qualified technician before restarting. If the indication only appears during a normal heating cycle, it is expected and not a safety issue.

Start by confirming whether the burner is actually firing or if the signal is a false reading. Check that all access panels are secured to eliminate extraneous light, and inspect the cad cell for soot or oil contamination, which can sometimes be resolved by carefully cleaning the cell face. If the cad cell resistance is out of range or the burner is not shutting off correctly, professional service is needed. Replacing a cad cell typically involves a low-cost part, but diagnosing a fuel valve or control issue requires a technician.