Lennox Furnace Error Code DS1 On / DS2 On

This code means the furnace control board has detected a condition consistent with a board failure or an incorrect wiring configuration. DS1 and DS2 are diagnostic indicators on the integrated furnace control board, and both being active simultaneously is a signal that the board cannot operate normally. The diagnostic process begins with checking that the board is receiving both 24V and 115V AC, then inspecting the control wiring before replacing the board.

When the DS1 On / DS2 On fault is active, the furnace control board is not functioning correctly and the furnace will typically not operate. Attempting to force operation is not advisable because the board manages critical safety functions including limit switches and ignition sequencing. Leave the furnace off until the fault is diagnosed and resolved.

Repair cost depends on the root cause. If the fix is simply tightening a loose connection or correcting a wiring error, a service call fee of roughly $80 to $150 may be all that is needed. If the integrated furnace control board requires replacement, parts alone typically range from $150 to $400 or more depending on the specific board, with additional labor costs on top of that. Getting a diagnostic visit from a licensed HVAC technician will clarify the exact cause and provide a firm repair estimate.

A knowledgeable DIYer can safely check whether the furnace circuit breaker is on and inspect visible wiring connections for obvious problems. However, confirming 115V and 24V supply voltages at the board requires a multimeter and comfort working around live electrical circuits, which carries real shock risk. Replacing the control board is a more advanced repair that requires matching the correct replacement part and carefully reconnecting all wiring harnesses. If you are not experienced with electrical diagnostics, a licensed HVAC technician is the safer choice.

A power reset may temporarily clear the code, but if the underlying cause is a failed control board or a wiring error, the fault will return as soon as the board attempts to operate. A reset is a reasonable first step to confirm whether the fault is intermittent, but it does not repair a failed board or fix a wiring problem. Proper diagnosis of the voltage supply and wiring is necessary for a lasting fix.