Homedics ultrasonic humidifier displays E4 and shuts down mist output shortly after starting.

Safety: Unplug the unit and remove the water tank before cleaning. Do not touch the transducer while powered.

Steps to resolve E4:

• Check water level: Ensure the tank is properly seated and filled to at least the minimum level so the transducer is fully covered during operation.
• Clean the transducer: Locate the metal ultrasonic disc in the base. Soak the disc area with a small amount of white vinegar for 5–10 minutes, then gently scrub with a soft brush or cotton swab. Do not use sharp tools. Rinse with clean water and dry the surrounding area.
• Inspect for cracks or discoloration: If the disc is cracked, heavily pitted, or burned, it may be failing and drawing excess current.
• Ventilation check: Make sure the air intake and exhaust grilles are not blocked by dust or objects, which can cause overheating.
• Test operation: Reassemble, refill, and run the unit. If E4 returns quickly, the transducer or its driver circuit is likely defective.
• Replace the transducer module: Many Homedics models use a replaceable ultrasonic transducer module with wires leading to the PCB. Unplug the unit, open the base, disconnect the transducer leads, remove mounting screws, and install the new module in the same orientation.
• Control board failure: If a new transducer does not resolve E4, the driver circuit on the main control PCB is likely damaged and the board or entire unit must be replaced.