Often the cause of dishwashing detergent remaining in the cup after a wash is something blocking the cup from opening. If the bottom rack of your dishwasher is loaded in such a way that anything is protruding, the cup may not be able to open and release the detergent. Place large plates and platters between the support pins and not over the outside edge. Load bowls, casserole dishes, pots and pans facedown at a slight angle. Face handles so that they don’t protrude through the bottom or the side of the rack. This can block the spray arm and the detergent cup. Large items should be placed at the sides, not across the front, to avoid blocking the detergent cup.
When dishwasher detergent gets old or becomes lumpy due to improper storage, it clumps. This clumping can prevent it from fully emptying from the dispensing cup during the wash cycle. Prevent clumping by storing dishwashing detergent in a cool, dry location. Under your sink is not an ideal place to store your detergent because this area typically is warm and moist, and moist detergent does not dissolve properly. Old detergent also tends to cake up and won’t properly dissolve either, leaving some behind in the dispenser cup after the dishwashing cycle.
To operate efficiently, your dishwasher requires water at a temperature of at least 120 degrees Fahrenheit. If your water heater is set lower than this, the soap may not dissolve properly and you may notice that your dishes aren’t coming as clean as they should. To determine if your water temperature is too low to dissolve the detergent, run the hot water in your sink until it reaches its hottest temperature. Then fill a glass with this hot water and add a tablespoon of detergent to the glass. If the detergent dissolves before it settles to the bottom of the glass, your water is hot enough and is not the cause of your problem. If it does not, set your hot water heater to at least 120 degrees so that the soap is fully dissolved during each use.
If the timer or relay switch doesn’t send a signal to the dishwasher controls indicating when it’s time to open the dispensing cup, it won’t open. An electrical malfunction can also prevent your dishwasher from completing a cycle, stopping the signal for the dispensing cup to open. This is a problem within the electrical components of your dishwasher and should be repaired by a qualified technician.