Most people assume a dishwasher works like a shower — clean water in, dirty water out, continuously. It does not. It fills with a few litres, then sprays that same water round and round for the entire cycle, straining the food out through a filter on every pass.
That single fact explains the symptom. When the filter blocks, the machine is no longer washing with dirty-ish water; it is recirculating a food slurry and spraying it onto everything. It takes food off one plate and puts it on another, which is exactly what people describe when they say the dishes come out worse than they went in.
Follow the water
Step 1 Understand why it got worse, not just dirty A dishwasher does not use fresh water throughout — it sprays the same few litres round and round, straining food out through a filter each pass. Block that filter and the machine recirculates dirty water, so it removes food from one plate and deposits it on another.
Step 2 Pull the bottom rack and twist the filter out The filter sits in the floor of the machine, usually under the lower spray arm. Most twist anticlockwise a quarter turn and lift straight out. There are commonly two parts: a coarse cylinder and a flat fine mesh beneath it. Take both.
Step 3 Rinse it under a hot tap and brush the mesh Hold it under running hot water and work an old toothbrush over the mesh from both sides. Do not use anything sharp — a torn mesh lets debris into the pump. Check that light passes through the mesh when you hold it up.
Step 4 Clear the spray arm holes Spin the lower arm by hand and look at each jet hole. Blocked ones are usually seeds, labels or limescale. Push a cocktail stick through from the outside and rinse. If the arm lifts off, take it out and flush it under the tap.
Step 5 Refit and run an empty hot cycle Seat the filter and twist until it locks — a loose filter lets debris bypass it entirely. Then run the hottest empty cycle with the machine empty to flush grease out of the pump and hoses.
Finding the filter
Open the door, pull the bottom rack right out, and look at the floor of the machine, usually under or just behind the lower spray arm.
You are looking for a plastic cylinder sitting in a round well. Almost all of them twist anticlockwise about a quarter turn and then lift straight up. Some have an arrow moulded into the top showing which way.
Underneath the cylinder there is normally a flat mesh plate as well. Lift that out too — it is the one that actually clogs, and it is the one people miss.
What you find under there is usually unpleasant: a grey paste of softened food, grease and label paper. That is normal, and it is the thing that has been sitting in your “clean” water.
Cleaning it properly
Hold the parts under a hot tap and work an old toothbrush over the mesh from both sides. Grease traps fine particles in the weave, and brushing only the top surface pushes them further in.
If it is heavily greased, leave the parts in hot water with a squeeze of washing-up liquid for ten minutes first.
Hold the mesh up to a light before you refit it. You should see light through the whole area. Dark patches are still blocked.
The spray arm, while you are down there
With the filter out, spin the lower spray arm with a finger. It should turn freely with a light push.
Now look at the jet holes along it. Blocked holes are extremely common and the culprits are always the same: fruit seeds, bits of label paper, and limescale. A blocked hole is a section of your dishwasher that simply is not being washed.
Push a cocktail stick or a thin wire through each blocked hole from the outside inward, then rinse. On most machines the arm lifts off after unscrewing a central cap by hand, which lets you flush it out properly under the tap.
Do the same for the upper arm if your dishes are dirtier on the top rack than the bottom.
Refit and flush
Seat the filter back in and twist until it locks. This matters more than it sounds: a filter that is sitting in place but not locked lets water bypass it entirely, so debris goes straight to the pump. It should not lift out without twisting.
Then run the hottest cycle with the machine completely empty. No detergent is needed, though a dishwasher cleaner or a cup of white vinegar on the top rack helps if it has been a long time. This flushes softened grease out of the pump and hoses rather than leaving it to redeposit on your next load.
If it is still bad
Work through these in order, because each rules something out:
- Water temperature. Dishwashers depend on genuinely hot water to emulsify grease. If the cycle finishes and the inside is not hot, suspect the heating element.
- Detergent age. Tablets lose enzyme activity after about a year, faster in a damp cupboard. Try a fresh box before assuming the machine is broken.
- Loading. Anything that shadows another item from the spray does not get washed. Bowls facing the centre, nothing overlapping, tall items not fouling the arms.
- Hard water. A white film rather than food residue is limescale — that needs salt, rinse aid and a descaling cycle, not filter cleaning.
If all four are fine and the filter is clean, the problem is likely the pump, the heating element or the water inlet — and that is the point where an engineer is cheaper than guessing.
The habit that prevents all of this
Scrape, do not rinse, and clean the filter monthly.
Scraping keeps the large debris out of the machine entirely. Not rinsing leaves enough residue for the detergent enzymes to work on — a perfectly pre-rinsed load genuinely can come out worse. And two minutes with a toothbrush once a month means you never have this problem at all.
The steps, in writing
Same sequence as the animation — handy if you'd rather read it, or print it and take it with you.
- Understand why it got worse, not just dirty A dishwasher does not use fresh water throughout — it sprays the same few litres round and round, straining food out through a filter each pass. Block that filter and the machine recirculates dirty water, so it removes food from one plate and deposits it on another.
- Pull the bottom rack and twist the filter out The filter sits in the floor of the machine, usually under the lower spray arm. Most twist anticlockwise a quarter turn and lift straight out. There are commonly two parts: a coarse cylinder and a flat fine mesh beneath it. Take both.
- Rinse it under a hot tap and brush the mesh Hold it under running hot water and work an old toothbrush over the mesh from both sides. Do not use anything sharp — a torn mesh lets debris into the pump. Check that light passes through the mesh when you hold it up.
- Clear the spray arm holes Spin the lower arm by hand and look at each jet hole. Blocked ones are usually seeds, labels or limescale. Push a cocktail stick through from the outside and rinse. If the arm lifts off, take it out and flush it under the tap.
- Refit and run an empty hot cycle Seat the filter and twist until it locks — a loose filter lets debris bypass it entirely. Then run the hottest empty cycle with the machine empty to flush grease out of the pump and hoses.
Questions people actually ask
How often does the filter need cleaning?
Monthly for most households, fortnightly if you rarely scrape plates or wash a lot of greasy pans. It takes two minutes once the filter is out. Almost nobody does it, which is why "my dishwasher stopped cleaning properly" is usually not a broken dishwasher.
Should I rinse plates before loading them?
Scrape, do not rinse. Large debris — bones, peel, rice — should go in the bin because it blocks the filter. But detergent enzymes need some food residue to work on, and a spotlessly pre-rinsed load can actually come out worse. Scraping is the right amount of effort.
There is a white film on everything instead of food.
That is a different problem — limescale or detergent residue rather than a filter blockage. Check the salt and rinse aid if your machine takes them, and run a cycle with a dishwasher cleaner or a cup of white vinegar on the top rack. Hard water areas need this every month or two.
The top rack is dirty but the bottom is fine.
The upper spray arm is not getting water or is not turning. Check that nothing tall in the bottom rack is fouling it, spin it by hand to confirm it moves freely, and check its holes for blockages the same way as the lower arm. Overloading is the most common cause by a wide margin.
I cleaned everything and it is still bad.
Check three things in order. Water temperature — dishwashers rely on hot water and a failing heating element means grease never emulsifies. Detergent age — tablets lose effectiveness after about a year and enzymes degrade in humid cupboards. And loading — dishes that shadow each other from the spray simply do not get washed. If all three are fine, it is time for an engineer.
Can I put the filter in the dishwasher itself?
No, and not because it would break anything — it just does not work. The filter sits below the spray pattern, so it never gets a proper jet. It needs the tap and a brush.