Heil furnace LED flashes 4 times; burners ignite but shut off quickly, or furnace cycles repeatedly without heating properly.

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

Steps to check:

• Check air filter: Locate the filter in the return air duct or blower compartment. If it is dirty or collapsed, replace with the correct size and airflow rating recommended for your Heil furnace.
• Inspect registers and ducts: Ensure supply registers and return grilles are open and not blocked by furniture or rugs. Check for crushed or disconnected ductwork near the furnace.
• Verify blower operation: Set the thermostat fan to "ON". The indoor blower should run continuously. If it does not start, or starts then stops, the blower motor or capacitor may be failing.
• Locate high limit switch: Typically mounted on the heat exchanger panel inside the burner compartment with two wires. Check for loose connections or signs of overheating.
• Reset and test: After correcting airflow issues, restore power and call for heat. Monitor operation to ensure the furnace runs a full cycle without tripping the limit.

When to call a pro: If the limit continues to open with a clean filter and good airflow, or if the blower motor is not running properly, contact an HVAC technician to test static pressure, blower speed, and replace the limit switch or motor as needed.