Furnace shuts down; LED flashes 13 times.

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

Chronic overheating due to airflow restriction, Undersized ductwork, Faulty limit switch, Control board lockout

Safety: Turn off power before accessing internal components.

Address airflow: Replace filters, open vents, and ensure return air paths are not blocked. Check for crushed or undersized ducts.
Inspect limit switch wiring: Verify all limit and rollout switches in the series circuit have secure connections.
Reset furnace: Turn off power for at least 5 minutes to clear lockout, then restore power and test.

If the furnace repeatedly enters limit lockout, have a professional evaluate duct design, blower sizing, and heat exchanger condition.

Hard 4/5

High Limit Switch

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