If your dishwasher has water sitting in the bottom even when you're not using it, there are a few potential reasons for this:
Drainage issues: The most common cause of water remaining in the bottom of the dishwasher is a drainage problem. There could be a clog or obstruction in the dishwasher's drain hose or the drain pump, preventing the water from fully draining out after a cycle.
Air gap or garbage disposal blockage: Some dishwashers are connected to an air gap or a garbage disposal unit. If these components are clogged or not functioning correctly, they can cause water to back up into the dishwasher.
High drain loop: Dishwashers typically have a high drain loop, which is a part of the drain hose that prevents wastewater from flowing back into the dishwasher. If the high drain loop is not installed properly or becomes disconnected, water can accumulate in the dishwasher.
Faulty check valve: The check valve is a one-way valve that allows water to flow out of the dishwasher but prevents it from flowing back in. If the check valve is faulty or stuck, it can cause water to remain in the dishwasher.
Malfunctioning float switch: The dishwasher's float switch is responsible for detecting the water level inside the tub. If the float switch is faulty or stuck in the "up" position, the dishwasher may think it has water in it even when it doesn't, leading to unexpected water accumulation.
To troubleshoot and address the issue, you can try the following steps:
Check for clogs: Inspect the drain hose, air gap, and garbage disposal for any clogs or obstructions. Clean out any debris you find.
Verify the high drain loop: Ensure that the dishwasher's drain hose is installed with a high drain loop according to the manufacturer's instructions.
Test the check valve: If accessible, check the check valve for any signs of damage or obstruction. Make sure it moves freely and closes properly.
Examine the float switch: Locate the dishwasher's float assembly and make sure it moves up and down freely. Clean any debris that may be affecting its operation.
Run a diagnostic cycle: Some dishwashers have a diagnostic mode that can help identify issues. Refer to your dishwasher's user manual for instructions on how to enter the diagnostic mode.
If you've tried these steps and the problem persists, it's best to contact a professional appliance repair technician to diagnose and fix the issue accurately.