Furnace LED flashes code 23; inducer runs but ignition does not proceed. Often associated with pressure switch stuck closed or open at wrong time.

Safety first: Turn off power before servicing. Do not bypass safety switches for operation.

• Inspect tubing: Locate the pressure switch mounted near the inducer. Remove the small rubber or silicone tube and check for moisture, kinks, or blockages. Blow gently through the tube to clear debris, then reconnect firmly.
• Check condensate drain: On high-efficiency Day & Night furnaces, inspect the condensate trap and drain lines for clogs or standing water. Clean the trap per manufacturer instructions and ensure the drain line slopes properly.
• Verify vent termination: Go outside and confirm the intake and exhaust terminations are clear of snow, leaves, or nests.
• Reset power: After cleaning, turn power OFF for 60 seconds, then ON, and call for heat.

If code 23 persists, the pressure switch may be out of calibration or the inducer may not be producing adequate draft. Replacement of the pressure switch with the correct rating for your Day & Night model should be done by a technician.