DIAGNOSIS The red exclamation point is a generic hardware error. The most common cause is a problem with the brush head sensor or a short circuit from moisture.
FIX Remove the brush head, dry the metal connector pin on the handle and the inside of the neck thoroughly with a cotton swab. Let it air dry for an hour. Reattach a different, clean brush head if you have one.
IF THAT DIDN'T WORK The error can also be triggered by a failing battery or internal damage from being dropped. Try placing it on the charger for a full 24 hours. If the error persists after a long charge, the unit likely needs service.
HEADS UP Never store the handle lying in water in the charging cup. Always shake off excess water and store it upright. This error often recurs if the internal sensor gets corroded.