Amazon Smart Thermostat Short Cycling Due to Limit or Flame Sensor Issues

Thermostat shows heat is on but furnace shuts off after a few minutes and restarts repeatedly

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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 furnace filter causing overheating, Blocked supply or return vents, Faulty flame sensor or high-limit switch (furnace issue, not thermostat)

How to Fix / Troubleshooting

Safety: Turn off furnace power at the breaker before opening panels.

  • Replace filter: Install a clean air filter of the correct size and type.
  • Check vents: Ensure all supply and return vents are open and unblocked.
  • Observe furnace LED codes: Many furnaces flash diagnostic codes indicating limit or flame sensor problems. Refer to the furnace manual.

If short cycling continues with a clean filter and open vents, a furnace technician should inspect the limit and flame sensing circuits. The thermostat is rarely the cause of this symptom.

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Repair Difficulty

Hard 4/5

Required Part

Furnace High-Limit Switch or Flame Sensor (not part of thermostat)
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