Furnace starts, inducer and burner run briefly, then shuts down and blower runs continuously; status LED shows code 33 (limit circuit fault).

Safety first: Turn off power to the furnace at the service switch and shut off gas at the gas cock before removing panels. Allow the furnace to cool completely.

Steps to check and correct:

• Inspect and replace filter: Remove the blower door, locate the return air filter, and check if it is dirty or collapsed. Replace with the correct size and airflow rating recommended for your Keeprite furnace.
• Check airflow restrictions: Make sure all supply registers and return grilles are open and not blocked by furniture, rugs, or debris. Inspect ductwork near the furnace for crushed or disconnected sections.
• Inspect high limit switch: Locate the primary high limit switch on the heat exchanger panel. Check wiring connections for looseness or burns. With power off, gently tug on connectors to ensure they are tight.
• Check blower operation: Restore power and call for heat. Verify that the indoor blower starts on time and runs at normal speed. If the blower is slow, noisy, or fails to start, the motor or capacitor may be failing.
• Reset rollout switches (if manual reset type): Some Keeprite models have manual-reset rollout switches near the burners. With power off, press the small red reset button if present. If it trips again, stop and call a professional—this indicates a serious combustion or venting problem.

When to call a technician: If the limit or rollout switch continues to open after filter and airflow issues are corrected, or if you suspect a cracked heat exchanger or undersized ductwork, contact a qualified HVAC technician.