An effective way to clean your coffee maker of mold is vinegar. Aside from its sanitizing properties, it can also decalcify or remove the mineral buildup caused by hard water.
Many coffee makers have mold and yeast growing in their water reservoirs. They may also contain bacteria. The moist environment of coffee maker reservoirs is perfect for mold and bacteria to grow in numbers.
Hot water alone will not be enough to get rid of the organisms. Your best bet would be bleach but you may have safety concerns in using it on your coffee maker. That leaves vinegar the next best thing to use.