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

This LED pattern indicates either a circuit board failure or an incorrectly wired control board. The control board is the main processing component that manages all furnace operations. The code tells a technician to start by checking that all wiring to the board is correct, and to replace the board if the wiring is found to be properly connected.

A furnace displaying this fault code will typically not operate normally, as the control board is responsible for managing ignition and safety shutoffs. Attempting to bypass or ignore the fault is not recommended, since a failed or miswired control board may not properly monitor safety circuits such as limit switches and pressure switches. The furnace should be inspected and repaired before continued operation.

A power cycle reset may temporarily clear the LED display, but the fault will return if the underlying cause, either incorrect wiring or a failed circuit board, has not been corrected. Repeated resets without addressing the root cause will not resolve the problem and may mask diagnostic information. The wiring and board condition should be inspected and resolved before relying on a reset.

A knowledgeable DIYer can inspect wiring connections at the control board for obvious issues like loose connectors, swapped terminals, or visible wire damage. However, if the wiring is correct and the board itself has failed, replacing a furnace control board involves working with line voltage wiring and gas system components, which is best handled by a qualified HVAC technician. Incorrect wiring during a board replacement can cause further damage or create safety hazards.

If the issue is simply a loose or incorrectly connected wire, the repair cost is primarily a service call fee, typically ranging from $75 to $150. If the control board requires replacement, parts and labor combined can range from $300 to $700 or more depending on the specific board model and your location. Getting a written estimate before authorizing the repair is advisable.