LED flashes code 23; furnace may not respond to thermostat or may cycle oddly.

Safety: Turn off power before working near the inducer or pressure switch. Do not bypass the pressure switch for operation.

Steps:

• Inspect pressure switch tubing: Remove the small rubber hose from the pressure switch and inducer port. Check for water, debris, or cracks. Blow gently through the tube to clear any blockage.
• Check pressure switch contacts: With power off, disconnect the wires and test continuity across the pressure switch. It should be open with no suction and close only when the inducer runs.
• Inspect inducer port: Ensure the nipple on the inducer housing where the tube connects is not clogged with rust or debris. Clean carefully with a small drill bit or wire (do not enlarge the hole).
• Observe inducer operation: Restore power and call for heat. Confirm the inducer motor starts smoothly and reaches full speed.

When to call a technician: If the pressure switch remains stuck closed or open despite cleaning, or if the inducer is noisy or not reaching speed, a technician should test draft and replace the faulty component.