Vinegar can be used to clean a Keurig coffee maker. However, should the machine become damaged from using vinegar, the one-year warranty may not cover repairs to it. If only the needles need cleaning, running a cycle without a pod until the water runs clear takes care of it.
The limited one-year warranty is explained in the pamphlet that comes with Keurig coffee makers and also on the Keurig site. To maintain the warranty, Keurig's brand of descaling solution must be used according to the directions on the back of that bottle.
Distilled white vinegar can be used only if ignoring the terms of the warranty. Cleaning a coffee maker requires approximately 48 ounces of vinegar, water and a timer. Place a large ceramic mug under the spout. Then pour the vinegar into the empty water reservoir. Run several cycles until Add Water is on the screen or lit. Allow the vinegar to sit in the machine for approximately four hours. After running the vinegar cycle, do the same thing with water. Be sure to empty the ceramic mug after each cycle.