Dishwashers were made to make washing dishes easier; if the machine isn't working properly, it becomes more of a chore for the homeowner. When the dishwashing soap doesn't dissolve completely, it can leave the dishes sticky and the inside of the dishwasher a mess. Soap won't dissolve for several reasons, such as the temperature of the water and a malfunction with the detergent cup.
Powdered dishwashing detergent dissolves better when you use hot water instead of cold or warm. If the water isn't hot enough when the dishwasher starts to fill or if the heating element isn't working correctly, the soap may not dissolve completely. Prior to running a cycle in the dishwasher, turn on the kitchen faucet and run the hot water for several minutes to make sure it gets hot. You can also have a professional technician test the heating element to make sure it's working properly.
Powdered dishwashing liquid absorbs moisture in the air quickly. It can clump together if it absorbs too much moisture in a short span of time. When these clumps harden, it can make it difficult for those clumps to dissolve during the wash cycle. It is best to keep the lid closed tightly and store the detergent in a cool, dry place to limit the amount of moisture it is exposed to.
When you have hard water, it doesn't dissolve dishwasher soap as easily as softer water. Getting a water softening system can solve the problem, but it is often expensive and you need to constantly replace the water softener as it runs out. You can also increase the temperature of the water via the water heater. It is also best to fill both detergent cups to give an extra boost of cleaning power.
If the soap in the dishwasher isn't dissolving properly, it is possible that the detergent cup isn't opening at the right time and the detergent isn't getting released at the right time. Because of this the detergent won't have a proper chance to dissolve. The cover of the detergent cup may not be opening completely during the wash cycle, trapping some of the detergent in the cup for the whole cycle. Inspect the cup and the cover for any damage or trapped buildup or debris. Wipe out the cup and cover with a rag and use white vinegar to clean them out completely.