Why Is My Roborock S8 Pro Ultra Dock Not Refilling the Water Tank?

Problem Description

Your Roborock S8 Pro Ultra dock is not automatically refilling the robot water tank before mopping. The robot starts mopping with an empty or low tank even though the dock clean water tank is full. The auto-refill feature is one of the main benefits of the Ultra dock but it stopped working leaving dry streaks during mopping.

Why This Happens in Real Homes

When a Roborock S8 Pro Ultra dock doesn't refill the robot's onboard water tank, the water path from the dock's clean-water reservoir to the robot is blocked or not connecting — usually an empty or unseated clean-water tank, a clog in the refill nozzle, or the robot not docking fully so the refill ports don't meet. The robot then mops dry.

Fill and firmly seat the dock's clean-water tank, then check the dock's refill nozzle and water path (and the robot's tank seating) for clogs or debris, cleaning any filter screen. Make sure the robot docks completely so the refill contacts align. A power-cycle of the dock and robot resets a stuck refill pump. With a full reservoir and a clear, connected water path, the dock tops up the robot between mopping passes.

Symptoms

• Dock won't refill the robot's water tank
• Mop tank stays empty
• No water for mopping
• Dock clean-water tank full but no refill
• Robot mops dry
• Refill cycle doesn't run
• Water not dispensing to the robot
• Dry mop pads

Recognize these? Here's what usually causes it.

Common Causes

• Dock clean-water tank empty or not seated
• Clog in the dock's water path/refill nozzle
• Robot's water tank not seated
• Refill valve/pump issue
• Robot not fully docked
• Water filter/screen clogged
• Debris blocking the refill contacts
• Firmware/pump glitch

Tools & Requirements

Step-by-Step Solution

1

Check Dock Clean Water Tank

Remove the clean water tank from the dock and verify it has water. The tank should be at least one third full for the pump to work properly. Also check that the tank is seated correctly with the outlet valve aligned to the dock port. An improperly seated tank will not dispense water even if full.

2

Verify Auto-Refill Setting

Open the Roborock app and go to your robot settings. Find the Dock settings section and confirm Auto-Refill or Auto Water Refill is enabled. Some firmware updates can reset this setting to off. Also check if there is a water refill schedule that might be preventing immediate refills.

3

Clean Robot Water Inlet Port

Remove the robot water tank and locate the water inlet port where the dock pumps water in. This small port can get clogged with mineral deposits or debris. Use a cotton swab dampened with water to clean inside the port. Also clean the rubber gasket around the port that creates the seal with the dock.

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4

Prime the Dock Water Pump

If the dock pump has air in the line it cannot push water. Remove the clean water tank and refill it completely. Reinstall it and use the app to manually trigger a water refill cycle. You may need to run this 2-3 times to push air out of the pump line. Listen for the pump sound and water flowing.

5

Check Robot Tank Float Sensor

The robot has a float sensor inside its water tank that detects water level. If this sensor is stuck in the up position the robot thinks the tank is full and rejects refills. Remove the robot water tank and shake it gently to free any stuck float. Fill and empty the tank manually a few times to exercise the sensor.

Quick Solutions

Still having issues? This is usually the deeper cause below.

Need More Help? Roku Support

Note: The contact information below connects you directly to Roku's official customer support team, not Trunetto. They can help with warranty claims, device replacements, and advanced technical issues.