Standing water in the bottom of a dishwasher is one of the few appliance faults where the homeowner fixes it more often than the technician does. The water has one way out, and the blockage is usually in a place you can reach with a towel and ten minutes.
Work the path in order. Every step is upstream of the next.
1. The filter, if the machine has one
Most dishwashers made in the last decade have a removable filter in the floor of the tub — usually a cylinder you twist out plus a flat screen under it. Older machines had a hard food grinder instead and no user filter at all. If yours has one and it has never been cleaned, that is very likely the whole problem.
Rinse it under hot water with a soft brush. While it is out, clear the sump underneath — glass chips, a fruit sticker and a wine cork are the classics, and any one of them will stop a drain pump.
2. The disposal, and the plug nobody removed
If the dishwasher drains into a garbage disposal, run the disposal first — a clogged one backs water straight into the dishwasher.
And if this is a new dishwasher that has never drained properly, check the knockout plug. Disposals ship with a plug in the dishwasher inlet, it has to be punched out during installation, and it is the single most common miss on a self-installed machine. The symptom is a dishwasher that has never worked rather than one that stopped.
3. The drain hose: kinks and the high loop
The hose has to rise to the underside of the counter before it drops to the drain, or it needs an air gap fitting on the sink deck. That loop is what stops sink water siphoning back into the tub. It gets knocked down when someone stores cleaning supplies under the sink, and then the dishwasher appears to fill itself with dirty water.
Check the hose for a crushed section too, especially where the machine was pushed back into its opening.
4. The air gap on the sink
That small chrome cylinder beside the faucet is a drain fitting, not decoration. Pop the cap, unscrew the cover, and look inside — they pack with debris and they are trivially easy to clean. Water spitting out of it during a cycle is the giveaway.
What is left is the machine
If all four are clear and it still holds water, the fault is internal: a drain pump with a jammed or failed impeller, a check valve stuck shut, or a control problem where the pump never gets told to run. You can usually tell the difference by ear — a pump that hums without moving water is jammed, and a pump that is silent during the drain portion of the cycle is not being energised at all.
Bail the water out before anyone works on it, and pull the plug rather than trusting the door switch.
Keeping it drained
- Scrape plates; do not pre-rinse them spotless. Modern detergents need something to work on, but bones and labels belong in the bin.
- Clean the filter monthly. It takes two minutes.
- Run the hot tap at the sink before starting a cycle, so the machine starts with hot water.
- Run a cleaner through the machine a few times a year, especially with hard water.
If it is the pump or the valve, that is dishwasher repair and usually a single visit — call (617) 404-9944. Commercial machines fail differently and the stakes are higher: see when a dish machine stops sanitizing.
