E4
Aprilaire
Control Internal Fault / EEPROM Error
Aprilaire digital humidifier control shows E4 and humidifier does not respond to call for humidity
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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
Corrupted control firmware, Voltage spike or brownout, Internal memory failure, Incorrect transformer voltage to control
How to Fix / Troubleshooting
Safety first: Turn off power at the furnace/air handler switch or breaker.
- Check transformer voltage: With power on and using a multimeter, verify the Aprilaire 24 VAC transformer feeding the control is providing 24–28 VAC between R and C. Low or high voltage can corrupt the control.
- Inspect wiring: Confirm R and C are not reversed or shorted to other terminals. Look for loose strands that could cause intermittent shorts.
- Power reset: Remove power for 5 minutes to fully discharge the control, then restore power and check if E4 clears.
- Surge protection: If the home has frequent power issues, consider adding surge protection to the HVAC circuit to prevent repeat failures.
- Replace control: If E4 persists, the internal memory/processor is likely damaged. Replace the Aprilaire digital humidifier control and reconfigure settings.
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Repair Difficulty
Medium
3/5
Required Part
Aprilaire Digital Humidifier Control
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