CTC Short Cycling

Furnace starts and runs briefly, then shuts off and restarts repeatedly (short cycling).

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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

Oversized furnace, Dirty air filter causing limit trips, Blocked vents or returns, Thermostat located in draft or near heat source

How to Fix / Troubleshooting

Safety first: Turn off power before removing panels.

Steps:

  • Replace the air filter with a clean one of the correct size.
  • Ensure all supply registers and return grilles are open and unobstructed.
  • Check thermostat location; avoid placing it near supply registers, direct sunlight, or exterior doors. Relocation may be needed by a professional.
  • Observe the furnace: if it shuts down on high limit (blower continues to run), airflow issues are likely. If it shuts down quickly without overheating, thermostat or control issues may be present.
  • Persistent short cycling should be evaluated by an HVAC technician to check furnace sizing and control operation.
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Repair Difficulty

Medium 3/5

Required Part

CTC High Limit Switch
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