Furnace attempts to start but shuts down; status LED flashes 2 times repeatedly on Armstrong Air furnace control board.

Safety: Turn off power to the furnace before opening panels. Do not bypass the pressure switch for operation; it is a critical safety device.

Steps to check:

• Inspect pressure switch tubing: Locate the rubber or silicone tubing from the inducer housing to the pressure switch. Remove it and check for water, debris, or kinks. Blow gently through the tube to clear obstructions and reinstall securely.
• Check venting and condensate: For high-efficiency Armstrong Air furnaces, inspect PVC intake and exhaust pipes for blockages (ice, leaves, nests). Ensure condensate trap and drain lines are not clogged, which can cause water to back up into the inducer and pressure tubing.
• Test pressure switch contacts: With power off, disconnect the wires and measure continuity across the pressure switch. It should be open when the inducer is off. If it reads closed with no inducer operation, the switch is stuck closed and should be replaced.
• Check inducer operation: Restore power and call for heat. Confirm the inducer motor starts and runs smoothly. If the inducer runs continuously even with no call for heat, suspect a control board fault.
• Replace faulty parts: If the pressure switch remains closed when it should be open, replace it with an Armstrong Air-approved pressure switch matched to your model and firing rate.