Dishwasher Not Draining? How to Clear It, and When to Call a Technician

Opening the dishwasher to a pool of grey water in the bottom is grim, but it is rarely the disaster it looks like. In most cases the pump is fine and something is simply in the way.

This guide walks through clearing it safely, then the five faults that cause it, in the order we actually find them. Two of them you can fix yourself this afternoon.

One note before you start: a small amount of clean water sitting in the sump under the filter is completely normal and is there by design to stop the seals drying out. What is not normal is water covering the bottom of the tub.

Clear the standing water first

You cannot inspect anything until the water is out. Switch the dishwasher off at the wall before you start, and have towels down.

Scoop what you can into a bucket with a jug or a cup, then soak up the last of it with towels or a sponge. It will smell, and there will be food debris in it. Once the tub is empty and dry you can see what you are dealing with.

1. A blocked filter

This is the most common cause by a distance, and it is entirely user-serviceable.

The filter sits in the floor of the tub, usually a cylindrical section that twists out, sometimes with a flat mesh plate underneath it. Twist it anticlockwise, lift it out, and take it to the sink.

What comes out is usually a mat of food debris, grease, labels off jars, seeds and broken glass fragments. Rinse it under a hot tap, scrub the mesh with an old toothbrush and a little detergent, and clear the recess it sits in as well. Refit it and make sure it locks in properly, because a filter that is not seated correctly lets debris straight into the pump.

If you are not cleaning this monthly, start. It is the single biggest factor in how long a dishwasher lasts.

2. A blocked or badly plumbed drain hose

The drain hose runs from the back of the machine to your sink waste or a standpipe. Two things go wrong with it.

It gets blocked, usually with grease that has congealed into a plug over years, most often at the point where it connects to the sink waste. Disconnect it into a bucket and check the flow.

Or it is plumbed wrong. The hose needs a high loop rising up under the bench before it drops to the waste. Without that loop, sink water can siphon back into the dishwasher, and the machine struggles to push water out. If your dishwasher has never drained properly since it was installed, this is very often why.

3. A blocked garbage disposal or new-installation air gap

If your dishwasher drains into a waste disposal unit, the dishwasher will not drain until the disposal is clear. Run the disposal and try again.

On a newly installed disposal there is a knockout plug that must be removed before the dishwasher hose is connected. If your dishwasher stopped draining immediately after a new disposal went in, that plug is the first thing to check.

4. A jammed or failed drain pump

If the filter and hose are clear and it still will not drain, attention turns to the pump.

Sometimes the impeller is simply jammed by a foreign object. Glass fragments, fruit stones, twist ties and small bones are the classics. You may hear the pump humming without moving water, which is the sound of a motor trying to turn a blocked impeller.

Sometimes the pump has genuinely failed and is silent. Either way, accessing the pump means tilting or partially dismantling the machine, and there is a live circuit involved, so this is where a technician should take over.

5. Control board, drain valve or float switch

The less common faults. A control board can fail to trigger the drain cycle at all, a drain solenoid valve can stick shut, and a float switch that is stuck in the raised position will convince the machine it is already full and stop it filling or draining correctly.

These present in ways that look alike from the outside, which is why chasing them by replacing parts on spec gets expensive quickly. They need testing rather than guessing.

When to call a technician

Book it in if any of these apply, rather than running the machine again and hoping.

CAI Appliance Services has repaired dishwashers across Perth for over 25 years, and we are the authorised service agent for several major brands. Our technicians are fully mobile and carry common parts on board, so most drainage faults are diagnosed and fixed in a single visit. Full details are on our dishwasher repair page.

• ✓The filter and drain hose are clear but water still sits in the tub
• ✓The pump hums but no water moves
• ✓The machine trips your power, or there is water under the cabinet
• ✓An error code returns after a full power-off reset
• ✓It has never drained properly since the day it was installed

How to stop it happening again

Scrape plates properly before loading, but do not pre-rinse them spotless, because modern detergents need some soil to work against.

Clean the filter monthly, run a hot cycle with a dishwasher cleaner every couple of months to shift grease from the hose, and check the spray arm holes are not blocked.

If your machine is getting on and drainage problems keep returning, it is worth asking whether a repair or a replacement makes better sense. If you do replace it, a correctly plumbed dishwasher installation with a proper high loop will save you this whole article next time.

Brand-specific notes

Bosch and Miele machines have excellent filtration but the filters do need regular cleaning to keep working as designed. Asko, Smeg, Dishlex and Blanco models are all common in Perth kitchens and all well supported for parts.

We service every major brand, so whatever is under your bench, we can look at it.

Dishwasher not draining: the quick version

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