Humidifier will not start; display shows E1 immediately after power-on.

Safety first: Unplug the Medisana humidifier from the mains before opening any covers. Do not work on the unit while it is connected to power.

• Power reset: Unplug the unit for 5 minutes, then plug it back in and try again. Sometimes E1 is a temporary sensor read error.
• Check sensor cable: Remove the top cover according to the user manual. Locate the small NTC sensor (usually a bead or metal tip on two thin wires) near the air intake grille. Ensure the sensor plug is firmly seated on the main PCB and that the wires are not pinched or broken.
• Inspect for corrosion: Look for green/white corrosion on the sensor connector. If present, clean gently with isopropyl alcohol and a soft brush, let dry fully, then reconnect.
• Test/replace sensor: If you have a multimeter, measure the resistance of the NTC sensor at room temperature (typically 5–100 kΩ depending on model). If it reads open circuit or 0 Ω, replace the NTC room temperature sensor assembly compatible with your Medisana model.
• If E1 persists: The sensor input circuit on the main control PCB may be defective. Replacement of the main control PCB is recommended and is best done by a qualified technician.