Heil furnace LED shows code 33; furnace shuts down on limit and blower may continue to run.

Safety: Turn off power before accessing blower or coil. If a rollout switch is involved, treat as a potential safety hazard.

Steps to check:

• Replace filter and check airflow: Install a clean filter and ensure all registers are open.
• Inspect blower operation: Set thermostat fan to ON. If blower does not start or is very weak, the motor or capacitor may be failing.
• Check evaporator coil: If accessible, inspect the underside of the A-coil above the Heil furnace for heavy dust or ice buildup. A clogged coil severely restricts airflow.
• Locate rollout switches: Visually inspect for tripped manual-reset rollout switches and signs of overheating. Do not repeatedly reset without professional inspection.

When to call a pro: Persistent code 33 requires a technician to measure temperature rise, inspect the heat exchanger and coil, and replace any defective limit or rollout switches and blower components.