Furnace shuts down; LED flashes code 13 indicating limit switch lockout or flame rollout lockout (depending on model).
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Critical safety warning: A limit or rollout lockout can indicate overheating or flame escaping the burner area. Turn off gas and electrical power to the furnace immediately. Do not continue to reset the furnace without finding the cause.
- Check air filter and airflow: Remove and inspect the furnace filter. Replace if dirty. Ensure all supply and return registers are open and not blocked by furniture or rugs.
- Inspect rollout and limit switches: With power off and gas off, remove the burner compartment door. Locate the rollout switches near the burners and the primary limit on the heat exchanger panel. Press the reset button on manual-reset rollout switches if present. If a rollout switch is tripped, do not simply reset and walk away—this indicates a serious combustion problem.
- Check venting: Inspect the flue pipe for disconnections, blockages, or corrosion. For condensing models, check PVC vent and intake for obstructions (leaves, nests, ice).
- Restart and observe: Restore power and gas, then call for heat. Watch the burner flame. If flames lift, roll out, or appear yellow and lazy, shut down and call a professional.
If the code returns after basic airflow checks, have a qualified technician inspect the heat exchanger, burners, and vent system.