Code 13 — Furnace Limit Lockout

What does 13 mean?

This fault indicates that the furnace has experienced a limit lockout. This typically happens when the internal temperature of the furnace exceeds a safe operating limit, causing the system to shut down for safety.

• Restricted airflow (dirty filter, closed vents)
• Overheating due to mechanical failure
• Faulty limit switch
• Blower motor malfunction

Click steps to track your progress.

1. 1

   Check and replace dirty air filters to ensure proper airflow.

2. 2

   Verify that all supply and return air vents are open and unobstructed.

3. 3

   Turn off the furnace at the thermostat, then turn off power at the circuit breaker for 30 seconds, and restore power.

4. 4

   If the lockout continues, a qualified HVAC technician should inspect the furnace.