Nothing can ruin a great cup of coffee quicker than a machine that is crusty with scale build-up. Scale---or mineral deposits---form from the water you run through your Keurig coffee machine. If not cleaned regularly, the build-up can clog the lines in your machine and ruin the heating element. The manufacturer recommends you descale Keurig coffee makers once every six months for normal water conditions and once every three months if you live in an area with hard water.
Unplug the coffee machine and remove the cup.
Turn the coffee machine upside down over the sink in order to fully drain it of water. Be careful of the plug and avoid getting it wet.
Pour undiluted white vinegar into the reservoir up to the top edge of the viewing window.
Place a ceramic cup under the machine, plug it in and press "Brew" for a large cup. Pour the cups of vinegar into the sink and repeat the process until the reservoir is empty.
Remove the final cup of vinegar and empty it. Fill the coffee maker with clean water and allow it to sit for four hours, remaining on.
Unplug the machine and dump the water into the sink.
Fill up the reservoir with fresh, clean water and plug it in. Place the ceramic cup back on the drip tray and run multiple brews in order to rinse the machine of any remaining vinegar residue.
Some Keurig machines come equipped with a red warning light to let you know when it is time to descale your machine. You may need to refill the water reservoir a second time and run additional cups through to rid it completely of the vinegar residue.
Never submerge your coffee machine or the electrical wires in water---it can lead to electrical shock. Do not use a "K" cup when descaling; use only a ceramic cup.