DIAGNOSIS You've probably got it set to 'Thermal Carafe' mode, which turns the hot plate OFF, but the machine is still detecting a carafe on the plate and defaulting to 'Glass Carafe' mode (which keeps heat on).
FIX 1) Before you start brewing, press the 'Carafe' button until the icon on the display shows the glass carafe symbol (with the wavy heat lines underneath). 2) Ensure you are physically using a glass carafe, not the thermal one, for this setting. The thermal carafe should only be used when the thermal icon (no wavy lines) is selected.
IF THAT DIDN'T WORK There's a small sensor in the center of the hot plate. Make sure it's clean and dry. Coffee spills can make it think a carafe is always present.
HEADS UP Leaving the hot plate on with nothing on it will cause it to overheat and can trip a thermal fuse, leading to a more serious repair. Always select the right carafe mode.