Carrier Furnace Error Code 13

Code 13 on a Carrier furnace means the limit circuit has gone into lockout. This happens when the high-limit switch, draft safeguard switch, flame rollout switch, or blocked vent switch remains open for more than 3 minutes continuously. The furnace shuts down to prevent unsafe operation and will automatically attempt to reset after 3 hours. The underlying cause must be identified and corrected to prevent the lockout from recurring.

Code 13 involves safety devices that protect against overheating, blocked combustion gases, and flame rollout, all of which can be hazardous if ignored. It is not advisable to continue running the furnace without diagnosing the cause first. A flame rollout condition in particular can indicate a cracked heat exchanger, which poses a carbon monoxide risk and requires immediate professional inspection.

Repair costs vary widely depending on the cause. A simple filter replacement costs only a few dollars, while a blower motor replacement typically ranges from $300 to $600 including labor. Flame rollout switch replacement is generally $100 to $250, but if a cracked heat exchanger is discovered, repair or heat exchanger replacement can range from $500 to over $1,500. A service diagnostic visit to identify the cause usually costs $75 to $150.

The control board is designed to auto-reset after 3 hours, so the furnace may restart on its own. However, if the condition that triggered the lockout, such as restricted airflow or a blocked vent, has not been resolved, the furnace will detect the same fault and lock out again. Auto-reset should not be relied upon as a fix, only as a temporary measure while the root cause is investigated.

Start by following the diagnostic steps associated with code 33, which covers the limit circuit in detail. Check the air filter and replace it if dirty, confirm the blower motor is operating at full speed, and inspect the flue vent for blockages. If airflow and venting appear normal, each switch in the limit circuit should be tested for continuity to identify any that have failed in the open position.