Bosch Dishwasher Not Draining but No Blockage

So, you’ve checked your Bosch dishwasher for blockages but found nothing, yet water is still pooling in the base of your appliance and not draining properly.

While less common, there are various reasons why a Bosch dishwasher can fail to drain despite there being no blockage. We’ll walk you through those reasons in this guide, offering expert tips on how to resolve them.

However, before we start, make sure that you’ve checked all of the following for blockages since they are very common causes:

• The filter
• The drain hose (also that it’s not kinked or pinched)
• Garbage disposal
• Any pipework and plumbing connections

Great! Here’s why your Bosch dishwasher is not draining despite there being no blockages:

The drain pump is damaged or faulty

Various issues with the drain pump can occur that may result in the dishwasher not draining properly, such as a faulty motor, a broken impeller, problems with the wiring or connections, or other types of damage.

The drain pump works by using its motor to spin the impeller which pushes the water out from the dishwasher into the drain. The easiest thing to check first is the impeller, which you can do like this:

1. Unplug the dishwasher and turn off its water supply.
2. Remove the lower rack, spray arm, and then the filter.
3. Use a sponge, small jug, or turkey baster to remove any standing water in the base of the tub and the filter housing.
4. Inside the filter housing you’ll see the pump cover—a white plastic component that you can pull out. Remove the cover to reveal the impeller (a small fan-like component). Some older models require you to remove a screw first.
5. Remove any standing water from the impeller, inspect it for foreign objects such as broken glass, plastic, or other debris, and rotate it manually to check it spins freely.
6. Also, check that the impeller is not damaged, for instance, cracked or has missing blades.
7. If there were foreign objects inside, that you’ve now removed, it spins freely, and there are no signs of damage, reassemble the dishwasher and run a test cycle to see if it now drains.
8. Unfortunately, if the impeller is damaged you will need to replace the entire drain pump. You cannot just replace the impeller.

So you’ve checked the impeller, now here’s how to check the rest of the drain pump and replace it if necessary.

1. With the dishwasher still unplugged and no water supply, remove the kick panel on the bottom of the appliance to access the drain pump.
2. Locate the drain pump under the filter housing.
3. Inspect the drain pump for signs of leaking water, cracks or damage to its housing, or loose, disconnected, or corroded wires.
4. Reconnect any loose or disconnected wires and clean or replace any wires which have corroded connections. If you believe the wiring was the issue, you can reassemble the dishwasher and run a test cycle after fixing the wiring.
5. If the drain pump or impeller is damaged, disconnect the wires and drain hose connected to the pump. Catch any water with towels or a container that comes from the hose.
6. Remove any screws or clips securing the drain pump in place, then remove it.
7. Purchase a new compatible drain pump, install it in place of the old one and run a cycle to see if the issue is now resolved.

There’s an issue with how it’s been installed

Various things can be done incorrectly during the installation phase of your dishwasher, potentially resulting in it not draining properly.

Even if you’ve had your dishwasher for a long time and it previously functioned well, something may have occurred—perhaps during home renovations, cleaning, or another activity—that has caused the appliance to no longer meet the installation requirements.

Here are some common installation problems that can result in drainage issues:

• The knockout plug on the garbage disposal hasn’t been removed. If so, disconnect the drain hose from the garbage disposal and knock out the plug with a hammer and screwdriver.
• The dishwasher is unlevel, causing water to pool in one side or corner of the tub and not drain. If so, use a spirit level and the dishwasher’s leveling legs to adjust the appliance until it’s level.
• If the drain hose is supposed to have a high loop, it may have become unattached from the countertop, may not be high enough, or may have been forgotten altogether during installation.
• If the drain hose is supposed to have a sink air gap, it may have been improperly installed, become blocked, or been missed altogether during installation.

Faulty check valve

The check valve is a small rubber component that sits under the pump cover in the filter housing. Its job is to stop drained water from flowing back into the dishwasher. However, if it is damaged or stuck in the wrong position, water can come back in, making it appear like the dishwasher isn’t draining.

Here’s how to inspect and replace the check valve:

1. Ensure the dishwasher is unplugged and that the water supply is shut off.
2. Remove the lower rack, lower spray arm, and filter.
3. Remove any standing water using a sponge, turkey baster, or container.
4. Remove the pump cover in the filter housing to access the check valve.
5. Locate and pull out the check valve. It looks like a small rubber flap.
6. Inspect whether it is damaged, dirty, or worn out.
7. If damaged, order a new one compatible with your Bosch model.
8. Clean the area where the check valve is located, then install the new check valve. It just slots into place.
9. Reassemble the dishwasher and run a cycle to see if it now drains.