my dumos keeps flashing the 'add water' light even though the tank is completely full to the max line.

Diagnosis

The "Add Water" indicator on the DUMOS Countertop Ice Maker is triggered by a magnetic float sensor located within the water reservoir. This sensor consists of a small, buoyant plastic cylinder (the float) that slides up and down a vertical guide rail. When the water reaches the "Max" line, the float rises, triggering a reed switch that tells the control board the tank is full. If the float becomes stuck in the "down" position due to friction, mineral buildup, or physical misalignment, the machine perceives the tank as empty regardless of the actual water level. This issue is most frequently caused by calcium and magnesium deposits (limescale) from hard water, which create a gritty residue on the guide rail, effectively "gluing" the float in place. In some cases, a small piece of debris or a stray ice shard can lodge itself under the float, preventing it from ascending. You can confirm this by looking into the reservoir; if the water is at the Max line but the white plastic float is sitting at the bottom or halfway down the rail, the sensor is malfunctioning.

How to Fix It

To resolve the stuck sensor and clear the "Add Water" error, follow these precise steps:

1. Power down the unit and unplug it from the wall outlet to prevent any electrical shorts during the cleaning process.
2. Remove the ice basket and scoop to provide a clear view of the interior reservoir.
3. Locate the white plastic float sensor. It is typically a small, pill-shaped piece of plastic resting against the side wall of the water tank.
4. Using a clean cotton swab or a soft-bristled toothbrush, gently push the float up and down its track 10 to 15 times. You should feel a smooth, effortless glide. If you feel resistance, do not force it, as the plastic guide can crack.
5. Fill a bowl with a mixture of warm water and a small amount of white vinegar. Dip the cotton swab in this solution and scrub the vertical guide rail where the float slides. This dissolves the mineral deposits causing the friction.
6. Drain the reservoir completely by flipping the drain plug at the bottom of the machine.
7. Rinse the reservoir with fresh, filtered water to remove any remaining vinegar residue.
8. Refill the tank precisely to the "Max" line. Ensure the float is now resting at the top of its track.
9. Plug the unit back in and press the "On/Off" button. The "Add Water" light should now be extinguished.

If That Didn't Work

• Perform a Hard Reset: Unplug the machine from the power source for at least 30 minutes. This allows the internal capacitors on the control board to discharge fully, which can clear "ghost" error codes that persist even after the float has been freed.
• Deep Descale Cycle: If the float moves but the light remains, there may be buildup inside the internal pump intake. Mix one part white vinegar with three parts water and fill the reservoir. Run the machine for one full cycle (even if it produces "vinegar ice"), then discard the ice and run two cycles of plain filtered water to flush the system.
• Check for Air Locks: Sometimes an air bubble can trap the float or affect the pressure sensor. Gently tilt the machine 15 degrees to the left and right while filled with water to dislodge any trapped air pockets around the sensor housing.
• Inspect for Physical Obstructions: Use a flashlight to inspect the very bottom of the float track. If a small piece of plastic flashing from the manufacturing process or a mineral "stone" has fallen into the track, it will block the float from dropping and rising correctly. Use a toothpick to carefully fish out any debris.

Heads Up

• Use Filtered Water: To prevent future sensor failures, always use filtered or distilled water. Tap water with high mineral content will inevitably lead to limescale buildup on the float rail.
• Weekly Maintenance: Wipe down the interior reservoir once a week with a damp cloth to prevent biofilm and slime from creating suction that holds the float down.
• Avoid Overfilling: Never fill the water beyond the "Max" line; doing so can cause water to leak into the internal electronics or cause the float to jam against the top of the housing.
• Storage Tip: If you are not using the machine for more than 48 hours, drain the water completely and leave the lid open to dry. Stagnant water accelerates mineral crystallization on the sensor.