13
Ducane
Limit Circuit Lockout
Code 13, limit switch lockout, furnace will not heat until power is cycled
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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.
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Possible Causes
Repeated high limit trips due to airflow restriction, Faulty high limit switch on Ducane heat exchanger, Oversized furnace short cycling, Blower speed set too low
How to Fix / Troubleshooting
Safety first: Turn off power before removing panels or touching wiring.
- Step 1 – Correct airflow issues: Replace dirty filters, open closed registers, and ensure return grilles are not blocked.
- Step 2 – Inspect blower speed tap: On PSC blower motors, verify the correct speed tap is connected to HEAT on the Ducane board. Too low a speed can cause overheating.
- Step 3 – Reset lockout: Turn power off for 30 seconds, then back on. Observe a full heat cycle. If the code reappears, the limit switch or heat exchanger may need professional evaluation.
- Step 4 – Professional check: A technician should measure temperature rise across the furnace and compare to the rating plate.
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Repair Difficulty
Medium
3/5
Required Part
High Limit Switch
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