Lennox Furnace Error Code DS1 Off / DS2 On

This code indicates that the flame sense rod is detecting a flame rectification current below the minimum threshold of 0.23 microAmps. The furnace control board uses this signal to confirm the burner is lit, and a reading this low causes the board to flag a low flame signal fault. The most common reason for this is a contaminated or failed flame sense rod. Cleaning or replacing the rod is the recommended first step.

The furnace will typically shut down the burner when this fault is detected, which is a built-in safety response to an unverified flame signal. Continuing to attempt ignition cycles repeatedly without addressing the root cause is not recommended, as repeated failed ignition attempts can allow unburned gas to accumulate briefly. Resolve the fault before returning the furnace to normal operation.

A power reset may clear the fault temporarily and allow the furnace to attempt ignition again, but if the underlying cause is not corrected the code will return. The flame sense rod contamination or fault that produced the low signal will still be present, and the furnace will detect it again on the next ignition cycle. Cleaning or replacing the flame sense rod is required for a lasting fix.

Cleaning the flame sense rod is a repair many experienced DIYers can perform. The rod is typically held by a single screw and can be removed and cleaned with fine steel wool or emery cloth to remove oxidation. However, if cleaning does not resolve the fault, diagnosing low gas pressure, burner alignment, wiring faults, or a failing control board requires more advanced skills and tools, and a licensed HVAC technician is recommended for those steps.

If the flame sense rod only needs cleaning, there is no parts cost and a service call fee would be the primary expense, typically in the range of $80 to $150 depending on your area. A replacement flame sense rod is generally an inexpensive part, often in the $15 to $40 range, though labor brings the total service cost higher. If the control board is at fault, board replacement can range from $200 to $600 or more including parts and labor.