In most cases, a Keurig coffee maker stops working because it is clogged in places or experiencing mineral build-up. Cleaning and descaling with vinegar typically restores function.
When a Keurig does not brew a full cup of coffee, does not run water at all or leaves grounds in a cup of coffee, chances are it needs to be cleaned or descaled to remove built-up mineral residue. In many cases, the exit needle is clogged with coffee grounds. Cleaning it requires the removal of the funnel from the K-Cup holder, inserting a paper clip into the tube and moving the clip around to break up the clog.
Descaling the Keurig involves emptying the water reservoir and refilling it with undiluted white vinegar. Experts recommend running four large-cup brew cycles without using a K-cup and swapping the vinegar for fresh vinegar after each cycle. After leaving the brewer powered on for four hours, allowing the vinegar sufficient time to dissolve mineral build-up in the Keurig's valves and tubes, the leftover vinegar should be discarded and the reservoir refilled with water. Running a large-cup cycle or two removes any traces of vinegar from inside the Keurig. Descaling should be conducted every three to six months.