Carrier Furnace Error Code 13 — What It Means
Error code 13 on a Carrier furnace is a limit circuit lockout. This means the furnace detected an open high-limit switch or flame rollout circuit for more than 3 minutes and has shut down for safety. This is not a nuisance trip. It is a safety shutdown telling you the furnace overheated or flames rolled out of the burner area. You may also see code 33, which is the underlying limit circuit fault the control detects when it rechecks the circuit.
The furnace will not restart until you correct the condition that caused the overheat or rollout and reset the system. Most of the time this code points to restricted airflow that trapped heat in the cabinet, but it can also mean a flame rollout switch tripped due to abnormal combustion or venting problems.
Common Causes
- Restricted airflow across the heat exchanger A dirty filter, closed supply or return registers, dirty ducts or grilles, or a clogged evaporator coil can trap heat and trip the high-limit switch.
- Weak or insufficient blower performance A dirty blower wheel, failing blower motor, or weak capacitor prevents the blower from moving enough air to cool the heat exchanger.
- Tripped flame rollout switch Abnormal flame behavior or venting problems can cause flames to roll out of the burner area and trip the rollout safety switch.
- Insufficient combustion air or venting problems On 90% condensing furnaces, blocked or improperly installed PVC intake or exhaust pipes can starve combustion or trap exhaust, and on 80% furnaces a tight closet can restrict combustion air.
- Plugged or damaged heat exchanger If flame rollout keeps happening, a cracked or blocked heat exchanger may be forcing flames out of the burner path, which is a serious safety hazard.
Step-by-Step Fix
- Turn off power to the furnace at the service disconnect and wait for all components to cool before working on the unit.
- Replace the air filter if it is dirty or restricted, then open all supply and return registers and inspect duct grilles for blockage.
- Inspect and clean the blower wheel by removing the blower assembly and checking for dirt buildup, loose blades, or damage that would reduce airflow.
- Check the evaporator coil (if present above the furnace) for dirt or blockage, and clean or replace it if restricted.
- Verify combustion air and venting by inspecting PVC intake and exhaust pipes on 90% furnaces for blockage or improper slope, and on 80% furnaces confirm the furnace has adequate ambient air and is not sealed in a tight closet.
- Reset the flame rollout switch (usually a red button near the burners) after it cools, then check for continuity to confirm it closes when reset, and replace it if it does not reset or close.
- Observe the flame with the burner door open and a call for heat: normal flames should be blue and directed into the heat exchanger tubes, but if flames are rolling out or dancing away from the burner area, shut the furnace down immediately and do not restart it until the heat exchanger is replaced.
Parts Often Needed
| Part | Notes |
|---|---|
| Carrier high-limit switch | Amazon | Required if the limit switch is faulty or does not close after cooling and resetting. |
| Carrier flame rollout switch | Amazon | Replace if the rollout switch will not reset or does not close after cooling. |
| Blower motor run capacitor | Amazon | Needed if the blower is weak or slow and the capacitor tests out of range. |
| Carrier blower motor | Amazon | Replace if the motor is failing or does not spin up to speed even with a good capacitor. |
When to Call a Pro
Call a licensed HVAC technician if you see flames rolling out of the burner area, if the rollout switch keeps tripping after you correct airflow problems, or if you are not comfortable working with gas appliances and electrical components. A cracked or damaged heat exchanger requires immediate professional replacement and is a carbon monoxide hazard. Also call a pro if you have checked all airflow paths and the limit keeps opening, or if you need to verify combustion air calculations or vent pipe sizing on a 90% condensing furnace.