E09
Alpha Low Temperature Limit / Freeze Protection Trip

Furnace shows E09; blower may run continuously and burners will not ignite.

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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

Return air temperature sensor failure, Open low-temperature limit switch, Control board sensing error, Extremely low ambient temperature in furnace area

How to Fix / Troubleshooting

Safety: Ensure the furnace is not exposed to freezing conditions that could damage the heat exchanger or condensate system.

  • Check furnace area: Verify the furnace is installed in a space within the temperature range specified by Alpha. Seal drafts and insulate if necessary.
  • Inspect low-temp sensor or limit: Locate the return air temperature sensor or low-temp limit on the blower compartment or return plenum. Ensure wiring is intact and the sensor is firmly mounted.
  • Power cycle: Turn off power for 5 minutes, then restore. Call for heat and observe if E09 clears.

If E09 persists in a normal-temperature environment, the sensor or control board may be faulty and should be tested and replaced by a technician.

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Repair Difficulty

Hard 4/5

Required Part

Alpha Return Air Temperature Sensor
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