F4
Keystone
Ultrasonic Transducer / Nebulizer Error (Humidifier Only)
Humidifier shows F4 and stops generating mist; fan may still run.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Failed ultrasonic transducer disc, heavy mineral scaling on transducer, open or shorted transducer wiring, failed driver circuit on main board
How to Fix / Troubleshooting
Safety: Unplug the humidifier and empty the tank before servicing. Do not touch the transducer while powered.
Steps:
- Clean the transducer: Access the water basin and locate the round metal ultrasonic transducer. Gently clean mineral deposits with a cotton swab dipped in white vinegar, then wipe with clean water and dry.
- Check for cracks: Inspect the transducer surface for cracks or pitting. A damaged disc must be replaced.
- Inspect wiring: If accessible, check the wires from the transducer to the control board for damage or loose connections.
- Replace transducer module: If cleaning does not restore operation, replace the ultrasonic transducer assembly with a Keystone-compatible part.
- Board failure: If a new transducer does not clear F4, the main control board driver circuit is likely faulty and requires replacement.
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Repair Difficulty
Medium
3/5
Required Part
Ultrasonic Transducer Assembly
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