Lennox Furnace Error Code LED#1 ON / LED#2 OFF

This LED pattern indicates either a circuit board failure or a control wiring error. The furnace control board uses this blink code to signal that it has detected a problem within its own logic circuits or with the wiring connected to it. A technician should inspect the wiring first, and if the wiring is correct, the control board will need to be replaced.

When the control board is flagging a fault with this LED code, the furnace may not operate correctly or at all, and safety circuits may not function as intended. It is not advisable to attempt to force the furnace to run in this condition. The furnace should be serviced before returning it to regular operation.

Resetting the furnace by cycling power may temporarily clear the displayed code, but if the underlying cause is a failed control board or incorrect wiring, the fault will return because the root problem has not been addressed. A reset is not a repair in this case. The wiring and board condition must be evaluated and corrected before the furnace will operate reliably.

A knowledgeable DIYer can inspect the control board wiring and compare it against the wiring diagram on the furnace cabinet to check for obvious errors, loose connectors, or misrouted wires. However, if the wiring is correct and the board itself has failed, replacing the control board requires identifying the exact replacement part for the furnace model and working safely around line voltage. Many homeowners prefer to have a qualified technician handle control board diagnosis and replacement.

If the issue is a wiring correction, repair costs are primarily the cost of a service call, typically in the range of $75 to $150 depending on your region. If the control board itself needs to be replaced, parts and labor combined can range from $300 to $700 or more, depending on the specific board required for your model and local labor rates.