Heil furnace LED shows code 45; furnace may lock out after multiple faults.

Safety: Identify and correct the underlying fault before repeatedly resetting the furnace.

Steps to check:

• Note prior codes: Many Heil boards will show a stored fault history. Observe which code occurred before 45 to identify the root cause (e.g., ignition, limit, pressure).
• Correct root issue: Follow the troubleshooting steps for the underlying code (e.g., clean flame sensor, replace filter, clear vent).
• Reset lockout: Turn off power to the furnace for at least 30 seconds, then restore. Call for heat and monitor operation.

When to call a pro: If the furnace repeatedly enters lockout, a technician should perform a full diagnostic to prevent unsafe operation and unnecessary wear on components.