Humidifier display shows letter 'F' and unit stops or will not start

Safety: Unplug the humidifier before handling the tank or base.

Steps:

• Check tank seating: Remove the water tank and reinstall it carefully, ensuring it sits flat and engages any alignment tabs or valves on the base.
• Inspect the float: On many BONECO ultrasonic and hybrid models (e.g., U700, U350, H300), a plastic float in the base detects water level. Remove the tank and look for the float in the base reservoir.
• Clean the float and chamber: If the float is coated with limescale or biofilm, it can stick. Clean the float and its guide with a soft brush and a solution of water and BONECO descaler or white vinegar. Rinse thoroughly.
• Check float movement: Move the float up and down gently. It should move freely and return smoothly.
• Inspect the float switch: Under the float, a reed switch or magnetic sensor is mounted on a small PCB. Ensure its wiring is intact and the board is not loose.
• Test after cleaning: Reassemble, fill the tank, and restart. If the 'F' error remains, the float switch assembly may be defective.
• Replace the float switch assembly: Install a new water level float and reed switch assembly designed for your BONECO model. Secure it in the same orientation and reconnect the wiring.