Carrier
Short Cycling Due to Overheating or Flame Loss
Furnace short cycles: burners ignite and run for 30–90 seconds, then shut off, restarting frequently.
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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 air filter, blocked supply or return ducts, faulty flame sensor, oversized furnace relative to duct system
How to Fix / Troubleshooting
Safety first: Turn off power before removing panels or filters.
- Replace or clean filter: Remove the existing filter and replace it with a clean one of the correct size and MERV rating. Avoid overly restrictive filters if ductwork is marginal.
- Open vents and returns: Ensure most supply registers are open and that return grilles are not blocked by furniture or rugs.
- Clean flame sensor: If burners light but shut off after a few seconds, clean the flame sensor as described in earlier entries.
- Check thermostat location: Make sure the thermostat is not directly above a supply register or in direct sunlight, which can cause rapid cycling.
If short cycling continues, have a professional check temperature rise, static pressure, and furnace sizing.
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Repair Difficulty
Medium
3/5
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