Control indicates 'Pressure Switch Open' or similar; inducer may run but burner will not light.

Safety first: Turn off power and gas. Risk of carbon monoxide exists with venting problems.

• Inspect vent and intake: Check all accessible vent and combustion air intake piping for obstructions, sagging, or disconnections. Clear any debris at terminations.
• Check inducer operation: With power restored, call for heat and verify the inducer motor starts and runs smoothly. If it hums or fails to start, the inducer assembly may be failing.
• Examine pressure tubing: Turn power off again. Remove the small rubber or silicone tubes from the pressure switch and inducer ports. Check for water, condensate, or debris. Blow through gently to clear and reinstall securely.
• Test pressure switch (basic): Listen for a click from the pressure switch shortly after the inducer starts. No click may indicate a faulty switch or insufficient draft.
• Do not bypass the switch: Never jumper the pressure switch for operation; this defeats a critical safety. If the fault persists, have a technician measure draft and replace the switch if necessary.