Fraser-Johnston
High Limit Trip Due to Restricted Airflow
Furnace ignites but shuts down after a minute or two; blower continues to run with cool air.
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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
Clogged filter, Blocked return air, Undersized ductwork, Dirty evaporator coil above furnace
How to Fix / Troubleshooting
Safety first: Turn off power before accessing internal components.
- Replace filter: Install a clean filter and ensure it is oriented correctly with airflow arrows.
- Check return grilles: Make sure return air grilles are not blocked by furniture or rugs.
- Inspect evaporator coil (if AC installed): Remove the coil access panel above the furnace and inspect for dust and debris blocking airflow. Coil cleaning is best done by a professional.
- Monitor operation: After improving airflow, run the furnace and see if it maintains burner operation without tripping.
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Repair Difficulty
Medium
3/5
Required Part
High Limit Switch
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