E3
Aprilaire
Relative Humidity Sensor Fault
Aprilaire digital humidifier control displays E3 and humidifier will not run in automatic mode
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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 internal RH sensor in control, Contaminants (dust, paint, chemicals) on sensor, Control installed in return duct with heavy condensation, Control circuit board failure
How to Fix / Troubleshooting
Safety first: Shut off power to the furnace/air handler before servicing the control.
- Inspect control environment: If the control is duct-mounted, check for condensation or water streaks around the mounting hole. Seal air leaks and insulate duct if needed.
- Check for contamination: Remove the control cover and inspect the RH sensor area (small vented section). If covered in dust or overspray, gently blow with dry compressed air. Do not use cleaners or water.
- Verify wiring: Ensure no low-voltage wires are pinched or shorted behind the control, which can damage the sensor circuitry.
- Reset control: Turn power off for several minutes, then restore. If E3 returns immediately, the sensor is likely failed.
- Replace control: Replace the Aprilaire digital humidifier control. Transfer each wire to the same terminal designation and set operating mode (manual/automatic) per the manual.
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Repair Difficulty
Medium
3/5
Required Part
Aprilaire Digital Humidifier Control
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