Scale, or calcium deposits build up in coffee makers and it is necessary to remove them.
It is important to descale your coffee maker periodically for optimum performance and flavor.
Some coffee makers have a cleaning indicator light, and others do not.
Signs that it is time to do so include: excessive brew times, gurgling or other unusual sounds, and changes in flavor.
Packaged descalers are widely available at retailers. Simply follow the directions on the package.
Affresh has available a tablet specifically designed for coffee makers.
You can also use a solution of a carafe of 1/2 vinegar and 1/2 water to descale.
It is very important to remove the water filter prior to descaling, so that it does absorb any residual tastes and odors, and to run cool water through the coffeemaker after descaling.