Detergent tends to build up over time and you may find that one day the detergent cup won't open. The detergent acts like glue, sealing the cup. Your dishwasher's detergent cup is located on the panel, inside your dishwasher's door. Grab your sponge and a bucket of warm water and clean the detergent cup inside and out. If this doesn't fix your problem, read on.

Let's understand how detergent cups work. The detergent is placed in the cup and the spring-loaded door is snapped shut. This keeps the detergent dry until later in the cycle. As the cycle progresses, a component will trigger the spring, allowing the door to open and the detergent to be released.

Not all dishwashers use the same components to open the detergent cup. Depending on your dishwasher the components in this process may include:

- Timer and bi-metal switch.
- Timer and wax motor.
- Timer.

The timer is responsible for the length of time your dishwasher runs each cycle. The timer sends an electrical current to each cycle component at a specific time and for a determined length of time. When the timer indicates it's ready for the detergent cup to open, it will send a current to a bi-metal switch or a wax motor. If your dishwasher doesn't have one of these components, the timer will activate the release of the door.

A bi-metal switch is an electrical component located behind the dishwasher detergent cup. This switch consists of two types of flexible metals bonded together to form one strip. An electrical current is sent to the bi-metal switch, heating the strip. Since the metals expand at different rates, the strip will bend. This action will open the detergent-cup door. A defective bi-metal switch won't expand enough to signal the release of the door and the switch will have to be replaced.

Many dishwasher manufacturers have replaced the bi-metal switch with a wax motor. There's actually wax inside this small motor. The timer sends a current and the wax inside heats up. As the wax heats up it expands and pushes on a piston. The pressure from the piston releases the spring and opens the detergent-cup door. If there's anything wrong with the wax motor, you may have problems with your dishwasher releasing the detergent.

If your dishwasher doesn't have a bi-metal switch or a wax motor, the timer also serves as an actuator. The timer activates a lever to release the door. If the lever is broken or damaged in some way, it's probably the culprit.

Test your bi-metal switch or wax motor if you have one. If you don't have one of these components or they aren't the source of the problem, test your timer. You may need to replace it.

Take care of your dishwasher and it will take care of you.