Diagnosis
The float sensor in the water tank cavity (inside the machine) is stuck in the 'down' position, or the contacts on the tank itself are dirty.
How to Fix It
Clean the sensor and contacts.
1. Remove the water tank.
2. Look inside the machine's cavity where the tank sits. You'll see a small white plastic float. Manually push it up and down a few times to ensure it moves freely.
3. Wipe the metal contact pins at the back of the cavity with a dry cotton swab.
4. Also dry the corresponding contacts on the back of the water tank.
If That Didn't Work
Mineral scale might be jamming the float mechanism. Descale the machine. If the error persists, the sensor itself may be faulty and requires service.
Heads Up
Always use the machine's handle to carry the full water tank. Pressing down on the tank lid can warp it, causing it to push the float down and trigger this false error.