Lennox Heat Pump Error Code Green ON / Red ON

The Green ON / Red ON LED combination on a Lennox heat pump indicates an internal component failure on the defrost control board. This is not a sensor or wiring fault but a failure within the board's own circuitry. The defrost board controls the cycle that prevents ice buildup on the outdoor coil, so this fault can impair normal heating and cooling operation.

Operating the heat pump with an active defrost control board fault is not recommended. A failed defrost board may prevent the outdoor coil from completing proper defrost cycles, which can lead to excessive ice buildup and potential compressor damage over time. It is best to have the system evaluated and the board replaced promptly.

Replacing the defrost control board is a task that a knowledgeable DIYer with electrical experience can perform, as it primarily involves disconnecting low-voltage control wiring and swapping the board. However, working inside a heat pump cabinet also involves exposure to line-voltage terminals, so caution and proper lockout procedures are essential. In many regions, certain heat pump repairs are restricted to licensed HVAC technicians, so check local regulations before proceeding.

The first step is to cycle the 24-volt power to the defrost control board, which performs a soft reset of the board logic. If the code clears after the power cycle, the unit may return to normal operation. If the Green ON / Red ON code comes back after the reset, the board has an unrecoverable internal fault and must be replaced.

Defrost control board replacement costs vary depending on the specific model and labor rates in your area. Parts alone typically range from around $80 to $300 or more for Lennox defrost boards, with total repair costs including labor generally falling in the range of $200 to $600. Getting a quote from a licensed HVAC technician for your specific unit is the best way to get an accurate estimate.