Furnace will not start; status LED shows 6 flashes repeating; blower may run continuously.

Safety: Disconnect power before accessing internal components. Do not operate the furnace with the venting disconnected.

Steps:

• Observe operation: Restore power and call for heat. Watch the sequence: inducer start, pressure switch close, ignition, flame, then monitor if the pressure switch opens mid-cycle (furnace shuts down and retries).
• Check vent terminations: Inspect outside terminations for intermittent obstructions (wind-driven debris, loose screens, insects). Remove any screens not approved by the manufacturer.
• Inspect pressure switch wiring: Ensure spade connectors are tight on the pressure switch terminals and at the control board. Repair any loose or corroded connections.
• Test pressure switch stability: With a manometer (technician tool), verify that inducer draft pressure stays within the rating printed on the pressure switch throughout the cycle. If pressure is marginal or drops, the inducer or venting may be restricted.
• Replace suspect parts: If draft is good but the switch opens intermittently, replace the pressure switch with the correct Concord-rated part.

Note: Persistent cycling lockouts indicate a system-level issue; professional evaluation of vent sizing and inducer performance is recommended.