Comfortmaker Short Cycling / Overheating or Oversized Furnace

Furnace starts and runs but shuts off before reaching the thermostat set temperature; frequent short cycles.

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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

Dirty filter restricting airflow, Closed registers causing high static pressure, Oversized Comfortmaker furnace for the home, Faulty high limit switch tripping early

How to Fix / Troubleshooting

Safety: Turn off power before removing panels. Do not bypass safety switches.

Steps:

  • Replace filter: Install a clean filter of the correct size and type.
  • Open registers: Make sure at least 80% of supply registers are open and unblocked.
  • Check return air: Ensure return grilles are not blocked by furniture or dust buildup.
  • Observe operation: Watch the burners and blower. If burners shut off and blower continues for a while, the high limit may be opening due to overheating.

When to call a technician: If short cycling continues with good airflow, a technician should check duct sizing, furnace sizing, and limit switch calibration.

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Repair Difficulty

Medium 3/5

Required Part

High Limit Switch
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