Dyson humidifier displays F9 and will not start misting cycle, even with full tank

Safety first: Unplug the unit and remove the water tank before inspection.

• 1. Check tank seating and valves: Ensure the tank cap is tight and the tank is fully seated so that the internal valve opens. If the tank is not engaging the base valve, water will not reach the pump.
• 2. Bleed airlock: Refill the tank completely, reinstall it, then gently rock the unit front-to-back (while unplugged) to help dislodge air bubbles in the internal water path.
• 3. Clean inlet filter: Some Dyson humidifiers have a small mesh filter or strainer at the water inlet in the base. If accessible, remove and rinse it under running water to clear debris.
• 4. Listen for pump: Plug in and start the unit. Listen closely for a faint buzzing or humming from the base. No sound suggests a failed pump or power supply to it.
• 5. Pump replacement: If F9 persists and the pump is silent or very noisy, the circulation pump assembly likely needs replacement, which requires opening the base and is a technician-level repair.