Furnace LED flashes code 33; burners may light briefly then shut off, blower runs continuously. Indicates limit or rollout switch open.

Critical safety: Flame rollout can indicate a dangerous condition. If you see signs of scorching around burners or smell strong combustion fumes, shut the furnace off and call a professional immediately.

• Check air filter and airflow: Replace dirty filters and ensure registers/returns are open to reduce overheating.
• Inspect rollout switches: With power OFF, locate the small manual-reset rollout switches near the burners. If they have a reset button, press it once to reset. If it immediately trips again, do not continue to reset.
• Look for visible blockage: Inspect the burner area for debris, rust flakes, or signs of flame impingement on the front of the furnace.
• Reset control: Turn power OFF for 60 seconds, then ON, and observe operation.

Repeated code 33 indicates a serious combustion or heat exchanger issue. A licensed technician must inspect the heat exchanger, venting, and burner alignment before further use.