Status LED flashes 4 times; furnace attempts to start but burners do not light or shut off quickly

Safety first: Turn off power before removing blower doors or reaching near moving parts.

• Replace or clean air filter: Locate the return-air filter (often in the blower compartment or return grille). Replace if dirty or clogged. Rheem furnaces are very sensitive to airflow restriction.
• Check vents and returns: Ensure supply registers and return grilles are open and not blocked by furniture, rugs, or debris.
• Inspect blower operation: With power restored, set the thermostat fan to ON. Verify the indoor blower starts promptly and runs at normal speed. Listen for squealing or grinding that may indicate a failing motor or capacitor.
• Locate high limit switch: The high limit is usually mounted on the heat exchanger panel with two wires. With power off, check for loose connections. If the furnace overheats and the limit opens repeatedly even with good airflow, the switch may be weak and require replacement.

Persistent high-limit trips can indicate a cracked heat exchanger or undersized ductwork; have a professional evaluate if the problem continues.