E3
Armstrong Air
Supply Air Temperature Sensor Fault
Armstrong Air communicating thermostat displays E3; furnace may not modulate correctly.
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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
Failed supply air sensor in furnace, Loose sensor connection on control board, Sensor shorted by condensation
How to Fix / Troubleshooting
Safety: Turn off power before accessing the blower or control compartment.
Steps to check:
- Locate supply air sensor: On some Armstrong Air furnaces, a thermistor sensor is mounted in the supply plenum or on the heat exchanger panel.
- Inspect wiring and connector: Ensure the sensor plug is fully seated on the control board and wires are intact.
- Check for moisture: Look for signs of condensation dripping onto the sensor or wiring. Correct any condensate leaks.
- Test or replace sensor: Compare sensor resistance to the temperature chart. If out of range, replace with the correct Armstrong Air sensor.
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Repair Difficulty
Medium
3/5
Required Part
Supply Air Temperature Sensor
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