Aprilaire dehumidifier displays E6 and will not respond to wall control

Safety first: Turn off power to the dehumidifier and wall control circuit before working on wiring.

• Inspect cable: Trace the low-voltage cable from the dehumidifier to the Aprilaire wall control. Look for staples through the cable, tight bends, or damage.
• Verify wiring order: At both ends, confirm that terminals (e.g., A, B, R, C) are wired to the same letters. Re-terminate any loose or crossed wires.
• Check for shorts: Remove the cable from both devices and test each conductor to all others with a multimeter. There should be no continuity between conductors.
• Test with short jumper: Temporarily connect the wall control to the dehumidifier with a short piece of known-good thermostat wire. If E6 clears, the original cable is defective and should be replaced with 18/2 or 18/4 thermostat cable per Aprilaire specs.
• Swap control if needed: If a known-good cable does not resolve E6, either the Aprilaire wall control or the dehumidifier main control board may be faulty and require replacement.