Furnace attempts to start but shuts down quickly; pressure switch error indicated.

Safety first: Turn off power and gas before removing covers or disconnecting tubing.

Steps:

• Locate the round or oval CTC pressure switch mounted near the inducer with small rubber or silicone tubing connected.
• Inspect the tubing for cracks, kinks, water accumulation, or disconnections. Replace damaged tubing and ensure tight fits on all barbed fittings.
• Check the flue and combustion air intake (if direct vent) from the furnace to the termination for obstructions such as leaves, nests, or ice. Clear any blockage.
• Remove the tubing from the pressure switch and the inducer port; gently clear the ports with a small drill bit or paper clip (do not enlarge the hole).
• Reassemble and restore power. Call for heat and listen for the pressure switch click as the inducer starts. If it does not close, the switch may be faulty.
• If the flue is clear and inducer is running but the switch will not close, replace the CTC draft pressure switch with the correct rating (inches w.c.) for your model.

Warning: Never bypass or jumper the pressure switch for normal operation; this is a critical safety device.