Display shows “ADD WATER” even though the reservoir is full; brewer will not start a brew cycle.

Safety first: Unplug the Keurig before removing parts or using water near electrical components.

• Check reservoir seating: Remove the water reservoir, empty it, rinse, then firmly reseat it. Make sure it is fully down and aligned with the base contacts or sensor window.
• Inspect the float: Look for a small plastic float or magnet inside the reservoir. Verify it moves freely up and down. If stuck, clean around it with warm soapy water and rinse thoroughly.
• Descale the sensor area: If there is a clear window or sensor area on the reservoir, clean it with a 1:1 white vinegar and water solution to remove mineral buildup. Wipe dry before reinstalling.
• Test without filter: Remove any charcoal water filter from the reservoir and try again; a mis-seated filter holder can interfere with water level.
• Check base contacts: On models with electrical contacts under the reservoir, gently wipe them with a dry cloth. Do not use excessive moisture.
• If still not detected: The internal water level sensor or reed switch may be faulty. At this point, professional service or replacement of the water level sensor assembly is recommended.