Furnace attempts to start but shuts down quickly; status LED shows 2 red flashes repeating; inducer may start, burners light briefly then go out.

Safety first: Turn off power to the furnace before opening any panels. Do not bypass safety switches for operation.

Steps to check:

• Inspect pressure switch tubing: Locate the round pressure switch near the inducer assembly. Remove the small rubber or silicone tube and check for water, debris, or cracks. Blow gently through the tube to clear any blockage. Reconnect firmly.
• Check vent and condensate (if high-efficiency): For 90+ AFUE Coleman furnaces, inspect PVC intake and exhaust pipes outside for ice, leaves, or nests. Ensure condensate trap and drain lines are not clogged or frozen.
• Test pressure switch contacts: With power off, disconnect the wires and check continuity across the pressure switch terminals. A normally open switch should show open with inducer off. If it reads closed with no inducer operation, the switch is stuck closed and should be replaced.
• Inspect inducer motor: Ensure the inducer wheel spins freely by hand. If seized, noisy, or not starting when power is restored and there is a call for heat, the inducer assembly may need replacement.

If the pressure switch continues to read closed when it should be open, replace it with a Coleman-approved pressure switch matched to your furnace model and venting configuration.