What This Error Means

Carrier Error Code 13 indicates that the furnace control board has detected repeated openings of the limit switch or flame rollout switch and has placed the system into a safety lockout. These switches are designed to stop furnace operation if unsafe operating conditions are detected. In most cases, the lockout is caused by restricted airflow that allows the furnace to overheat. A dirty air filter, blocked supply or return vents, a malfunctioning blower motor, or a failing limit switch are among the most common causes. Less commonly, a flame rollout condition or control board issue may be responsible. This lockout is a protective feature designed to prevent damage to the furnace and reduce the risk of unsafe operation. Before restoring normal operation, the underlying cause of the repeated safety switch openings should be identified and corrected.

Symptoms You May Notice

• The furnace stops producing heat and enters a safety lockout.
• The status LED flashes Error Code 13.
• The blower motor may continue running after the burners shut off.
• The furnace may attempt to restart before returning to lockout.
• The thermostat calls for heat, but the furnace does not complete a normal heating cycle.

Common Causes

• Dirty or restricted air filter
• Blocked supply or return vents
• Blower motor not moving enough air
• Limit switch opening because of overheating
• Flame rollout switch opening
• Faulty limit switch or flame rollout switch
• Control board issue

Safe Troubleshooting Steps

1. Turn off power to the furnace before performing any inspection.

2. Inspect the air filter and replace it if it is dirty or restricted.

3. Verify that all supply and return vents are fully open and not blocked by furniture, rugs, or other objects.

4. Check that the blower compartment and surrounding area are free of debris that could restrict airflow.

5. Restore power and attempt to restart the furnace.

6. If Error Code 13 returns after completing these checks, discontinue troubleshooting and contact a qualified HVAC technician.

Parts Commonly Involved

• Air filter – A dirty or restricted filter can reduce airflow and contribute to furnace overheating.

• Limit switch – Monitors furnace temperature and opens when excessive heat is detected.

• Flame rollout switch – Shuts down burner operation if flame or excessive heat is detected outside the normal combustion area.

• Blower motor – Moves air through the furnace and duct system; reduced airflow may contribute to this fault.

• Control board – Monitors the safety switches and places the furnace into lockout after repeated switch openings.

When to Call a Technician

If Error Code 13 returns after completing the recommended homeowner checks, additional diagnosis is needed. A qualified HVAC technician has the tools and training to safely identify electrical, airflow, combustion, or safety control problems that cannot be confirmed through a basic visual inspection.

Call a qualified HVAC technician if:

• The error returns immediately after resetting the furnace.
• The furnace repeatedly enters lockout.
• You notice a burning smell, smoke, or signs of overheating.
• The blower motor does not operate normally.
• A limit switch or flame rollout switch appears to be faulty.
• The manufacturer’s troubleshooting procedure requires electrical testing or component replacement.

Safety Notice

Error Code 13 indicates that one or more furnace safety devices have activated to protect the system from unsafe operating conditions. Do not continue resetting the furnace if the error repeatedly returns. Correct the underlying cause before returning the system to normal operation.

Manufacturer Documentation