Humidifier with warm-mist or hybrid mode shows F4 and stops heating, fan may still run.

Safety: Unplug the unit and let it cool completely. Do not bypass any thermal safety devices.

• Check for scale buildup: Remove the water tank and inspect the heating chamber (if accessible). Heavy limescale can cause localized overheating. Descale according to the Rowenta manual using a recommended descaling solution or white vinegar (if allowed by the manual).
• Verify water level: Ensure the tank is properly seated and filled to the correct level. Running the heater dry can trigger overheat protection.
• Clean air paths: Blocked airflow can cause internal overheating. Clean intake and exhaust grills.
• Internal checks (advanced): If you are experienced, you can test continuity of the heating element and thermal fuse with a multimeter after disassembly. Replace only with identical rated parts.
• If F4 returns: The heater assembly or control PCB likely needs replacement. Due to fire and shock risk, this repair is best left to an authorized service center.