Burners ignite but shut off quickly; status LED shows 4 flashes repeating.

Safety: Turn off power before working inside the blower compartment. Components may be hot immediately after operation.

Steps to resolve:

• Check air filter: Locate the return air filter (often in the blower compartment or return grille). If it is dirty or clogged, replace with the correct size and airflow rating recommended for your Concord furnace.
• Inspect supply and return registers: Walk through the home and ensure supply registers and return grilles are open and not blocked by furniture, rugs, or drapes.
• Verify blower operation: Call for heat and observe the blower motor. It should start within a minute or so after burner ignition. If the blower does not start, hums, or cycles on and off, the blower motor or capacitor may be failing.
• Inspect high limit switch: The high limit is usually mounted on the heat exchanger panel inside the burner compartment. Check wiring connections for tightness and signs of overheating. With power off, test continuity across the limit. If it is open when the furnace is cool, replace the limit switch.
• Check for duct restrictions: Inspect accessible ductwork for crushed sections, closed dampers, or disconnected runs that could reduce airflow.

Important: Do not bypass or jumper the high limit switch for operation. It protects against overheating and fire hazards.