DIAGNOSIS The three-beep error usually means the carafe isn't seated correctly on the warming plate or the brewer thinks it's missing. The sensor needs the carafe to be in the perfect spot.
FIX First, just lift the carafe off and set it back down firmly. You should feel it click into place on that little circular guide. If that doesn't stop the beeps, unplug the brewer for a full minute. Plug it back in, put the carafe back on, and try again. It's a simple reset that clears the sensor's memory.
IF THAT DIDN'T WORK Check the bottom of the glass carafe itself. If the little silicone pad on the bottom is worn out, missing, or covered in dried coffee gunk, it might not be making proper contact. Give it a good clean. If the pad is damaged, you'll need a replacement carafe.
HEADS UP This brewer is picky—it won't brew at all without the carafe in place, even if you just want to run a clean cycle. Always make sure it's seated before you hit any buttons.