Dehumidifier shows E4 and compressor does not run

Safety: Disconnect power before servicing. Do not spray water or cleaner directly on sensors or circuit boards.

Procedure:

• Locate humidity sensor: On Bionaire dehumidifiers, the RH sensor is typically mounted behind the front grille or near the air intake, often on a small daughter board or as a plastic-encased module.
• Visual inspection: Check for dust buildup, mold, or corrosion on the sensor. Lightly clean with dry compressed air or a soft brush. Do not use liquid cleaners.
• Check connections: Ensure the sensor’s plug is fully seated on the main PCB. Inspect the harness for damage.
• Functional test: If you have a multimeter and the sensor datasheet, verify that the sensor outputs change with humidity (often as a varying resistance or voltage). If not available, substitution with a known-good Bionaire humidity sensor is the most practical test.
• Replace sensor: If cleaning and reseating do not clear E4, replace the humidity sensor module with the correct Bionaire part.
• Control board: If a new sensor does not resolve the error, the main control PCB’s humidity input circuit is likely faulty and must be replaced.