Water left in the bottom of the dishwasher

A little moisture in the bottom after a cycle can be normal. Bosch, for example, says a small amount of water is expected on its machines. What we're talking about here is a real puddle that covers the bottom of the tub, or dirty water sitting there the next morning.

That's a drain problem, and the cause is usually somewhere between the filter and your sink drain. Work through these checks in order.

Before you reach into the tub, switch off the dishwasher's power at the breaker or unplug it. Have towels ready, and watch for broken glass in the sump.

1. Clean the filter

Start here. It's the easiest thing to fix. Bosch says a blocked or dirty filter can keep the dishwasher from draining, and that cleaning it often solves the problem.

1. Pull out the lower rack.
2. Twist and lift out the filter assembly at the bottom of the tub. Some machines have more than one piece. Samsung's filter system has three parts.
3. Rinse the filters under running water. Use a soft brush on the fine mesh.
4. Look into the opening under the filter and remove any food, seeds or bits of glass.
5. Put the filters back the right way. Bosch says to line up the arrow marks, and Samsung warns not to put the fine filter in upside down.

Bail out the standing water with a cup and towels if you need to reach the filter, then run a short cycle to see if it drains.

2. Run the garbage disposal

In most kitchens the dishwasher drains through the disposal or the sink drain. If that path is clogged, the dishwasher has nowhere to push water. iFixit recommends clearing the disposal and flushing it with cold water before you look further.

3. New install? Check the knockout plug

If the dishwasher is new, or the garbage disposal is new, this one is worth checking first. Disposals ship with a plug inside the dishwasher inlet, and it has to be knocked out when a dishwasher is connected. Whirlpool says the plug sits recessed inside the inlet, so you can't see it from outside.

Whirlpool's test is simple. With the power off, disconnect the drain hose from the disposal and push a pencil into the inlet. If it goes in about 3 inches, the plug is out. If it stops short, the plug is still there.

If your sink has an air gap, there's another clue. iFixit points out that water backing up through the air gap on a new install is a common sign the plug was never removed. Knocking it out means working inside the disposal inlet and fishing the loose piece out of the disposal afterward. If you'd rather not, we can handle it on a visit.

4. Check the drain hose under the sink

The drain hose should rise in a high loop before it drops to the disposal or drain. Whirlpool says the loop should be secured near the top of the cabinet wall or the underside of the countertop. A hose that runs flat or slopes down can let sink water flow back into the tub.

Also look for kinks and pinches along the whole hose. Dishwashers often get pushed back into the cabinet during install, and the hose folds behind them. Samsung says the hose should be straight with no kinks or bends.

5. Clear the air gap, if you have one

Some sinks have an air gap, a small fitting near the faucet that the drain hose passes through. iFixit notes that air gaps are required in some places and optional in others. If yours spits water during the drain, it's likely clogged. Whirlpool says to remove the cap and clear the blockage, following the air gap maker's instructions.

6. Drain pump and check valve

If the filter is clean and the path under the sink is clear, the problem is likely inside the machine. iFixit says a healthy drain pump should empty the tub in a few minutes, and that slow draining or standing water is a sign of a bad pump. A loud buzz can mean something is jammed in the pump. A scraping sound can mean a damaged impeller.

Many dishwashers also have a check valve that stops dirty water from flowing back into the tub. If it sticks closed, water can't leave. Some models use a small check ball instead, which can also stick.

Getting to the pump usually means pulling the dishwasher out and working underneath it, close to water and wiring. This is the point where we'd take over.

Keeping it from coming back

Most standing water problems start small. Samsung and Bosch both say to clean the filter regularly, and it only takes a couple of minutes once you've done it the first time. If your dishwasher drains through a disposal, keep that clear too, because the two share the same drain.

Any time someone works under your sink, take a quick look at the drain hose afterward. A plumber replacing a trap or a new disposal going in can leave the hose flat or kinked without anyone noticing.

When to call us

• The filter is clean, the disposal is clear, and water still stays in the tub.
• You hear humming or buzzing during the drain but water doesn't go down.
• Water leaks onto the floor, or you see water damage around the cabinet.
• An error code about draining keeps coming back.

Repair or replace?

Drain problems are usually some of the more straightforward dishwasher repairs. A clog, a hose or a drain pump is typically worth fixing. If the tub is rusted through or the dishwasher has other problems stacking up, we'll tell you after the $129 diagnostic and give you an honest recommendation either way.