Carrier Error Code 33: Limit/Rollout Switch Lockout

Error code 33 on your Carrier furnace signifies that the unit's control board has detected an open limit switch or rollout switch for longer than is considered safe. These switches are safety devices designed to shut down the furnace if it overheats or if flames are detected where they shouldn't be (like outside the burner box). The control board locks out after detecting this condition to prevent further operation until the issue is resolved. This lockout requires a manual reset, usually by cycling power to the furnace. This error is often triggered by a genuine safety concern, such as a blocked vent, a malfunctioning fan, or a cracked heat exchanger. It's crucial to address the underlying cause rather than simply resetting the furnace, as repeated lockouts could indicate a dangerous condition. Ignoring this error can lead to equipment damage, fire, or carbon monoxide poisoning.