Dishwashers that leave grit on plates, smell between cycles, or have gradually stopped cleaning as well as they used to have one thing in common far more often than any other: a filter that has never been taken out.
A surprising number of people don't know their dishwasher has one. It's at the bottom of the tub, under the lower spray arm, and it collects everything that comes off the dishes.
The Short Answer
How often depends entirely on whether you scrape plates before loading.
- You scrape thoroughly — check it monthly
- You scrape roughly, as most people do — every two weeks
- You load plates more or less as they come off the table — weekly
- Any load with rice, pasta, seeds or eggshell — check it afterwards regardless
Where it is: the bottom of the tub, beneath the lower spray arm. Usually a cylindrical section that twists out, sitting in a flat mesh plate that then lifts free.
The job: twist out the cylinder, lift the mesh, rinse both under a hot tap, use a soft brush on the mesh, wipe the recess they sit in, and refit. Two minutes.
Self-cleaning filters exist on some machines — usually those with a food macerator — but even those need periodic checking. "Self-cleaning" means it grinds waste small enough to drain, not that the filter never needs attention.
What Actually Matters
The water in a dishwasher is recirculated. This is the thing people don't picture. A dishwasher doesn't spray fresh water continuously — it fills once with a small quantity, then pumps that same water round and round through the spray arms for the whole wash phase.
The filter is what keeps that recirculating water clean enough to be worth spraying at your dishes. Blocked, you're spraying dirty water with food particles in it, which is precisely why the symptom is grit deposited back onto plates.
Restricted flow reduces spray pressure. The pump has to draw water through the filter. A clogged one starves the pump, spray arm pressure drops, and the top rack — which is furthest from the pump — suffers first. A dishwasher that cleans the bottom rack fine and the top rack badly is very often a filter problem rather than a spray arm one.
Trapped food is what smells. Organic matter sitting warm and damp in the filter recess between cycles produces the odour people blame on the machine or the drain. Cleaning the filter usually removes it entirely.
Detailed Analysis
Finding it and taking it apart
Open the door, pull out the lower rack, and look at the floor of the tub. Under or beside the lower spray arm there'll be a circular fitting, typically 60-80mm across, often with arrows or a padlock symbol indicating which way to turn.
Most designs have two or three parts:
The coarse filter — a plastic cylinder or cup that twists anticlockwise and lifts out. This catches the big items: labels, seeds, bits of pasta, the occasional cocktail stick.
The fine mesh plate — a flat filter that sits beneath, usually lifting free once the cylinder is out. This is the one that actually clogs, and it's the one people miss because it doesn't look like a removable part.
The micro filter — on some machines, a third finer layer bonded to the mesh plate. It comes out as one piece with the plate.
On some machines the spray arm has to come off first, which is usually a nut or a clip. If the filter won't come free, check whether something is holding it before applying force.
Cleaning it properly
Rinse both parts under a hot tap first, holding the mesh so the water runs through from the clean side to the dirty side. That pushes debris out rather than further in.
Use a soft brush — an old toothbrush is ideal — on the mesh. The fine holes clog with grease and fine particles that rinsing alone won't shift, and this is the step that makes the difference. Washing-up liquid on the brush helps with greasy build-up.
Don't use anything abrasive or a wire brush. The mesh is fine plastic or thin steel and damaging it means an unfiltered machine.
While the filter is out, look into the recess it sits in and wipe it. Debris collects there too, and it's the part most likely to be producing a smell. A cloth and a wipe round takes seconds.
Check the sump — the well at the bottom — for anything solid. Glass fragments, cherry stones and bits of broken crockery collect here and can damage the pump impeller.
Refit both parts and make sure the cylinder locks. A filter that isn't seated properly lets debris straight into the pump, which is a considerably more expensive problem.
Symptoms that point at the filter
Worth listing, because these get attributed to all sorts of other things.
- Grit or particles left on clean dishes — the classic sign
- Smell between cycles, particularly noticeable when the door is opened
- Top rack cleaning worse than the bottom — reduced pressure reaching the upper arm
- Standing water in the bottom beyond the normal small amount around the filter
- Cycle times lengthening on machines that sense water clarity
- A gradual decline over months rather than a sudden failure
That last one is the tell. Filter problems develop slowly, which is exactly why people don't notice and why they conclude the machine is getting old.
Rinsing versus scraping
Worth clarifying because it affects how often you'll be doing this.
Modern dishwashers with auto programmes measure how dirty the water is and adjust the cycle. Rinsing plates thoroughly before loading means the machine reads a light soil level and selects a shorter, cooler wash — which then struggles with whatever is actually there.
Detergent enzymes also need something to work on. Protease and amylase break down protein and starch, and on a rinsed plate they have nothing to do.
The right approach is to scrape, not rinse. Get the solids off into the bin — that's what keeps the filter clear — and leave the rest for the machine.
The things genuinely worth removing before loading are the ones that block filters fastest: rice, pasta, seeds, eggshell, and anything fibrous.
Real-World Considerations
The filter interacts with hard water. In hard water areas the mesh accumulates limescale alongside the grease, and it becomes stiff and less effective. Soaking the filter in a bowl of white vinegar for an hour every few months deals with this.
New machines are worse than people expect for the first few weeks, because manufacturing debris and packaging fragments end up in the filter. Worth checking after the first two or three loads.
If the filter clogs unusually fast despite scraping, look at what's going in. Anything that sheds — paper labels on jars, adhesive residue, tea leaves — accumulates quickly.
Machines with a food macerator or self-cleaning filter still benefit from a look. They grind waste rather than trapping it, which works well, but the grinding assembly can jam on something hard, and the mesh surrounding it still collects grease.
One thing worth building into a routine: check the filter at the same time as topping up the rinse aid and salt. It groups the three maintenance jobs a dishwasher needs into one occasion, which makes it far more likely to actually happen.
And a small point about smells specifically. If the filter is clean and the machine still smells, the next things to check are the spray arm jets, the door seal folds where debris collects, and the waste hose arrangement — a drain smell entering through the waste connection is a different problem with a different fix.
Common Mistakes Buyers Make
- Not knowing the filter exists. The commonest situation by a wide margin. Look under the lower spray arm.
- Cleaning the cylinder but not the mesh plate underneath. The mesh is the part that actually clogs.
- Rinsing without brushing. Grease in the fine mesh doesn't come out under a tap alone.
- Using a wire brush or scourer. Damages the mesh and leaves the machine effectively unfiltered.
- Not refitting it fully. A filter that isn't locked lets debris into the pump.
- Pre-rinsing plates thoroughly. Makes auto programmes select a weaker cycle and leaves enzymes nothing to work on.
- Assuming self-cleaning means no attention. It means the waste is ground rather than trapped, not that nothing accumulates.
- Blaming the machine for a gradual decline. Filter clogging develops over months and looks exactly like an ageing appliance.
Alternatives Worth Considering
A dishwasher cleaner run through an empty hot cycle every couple of months deals with grease in the parts you can't reach — the pump housing, the internal pipework and the spray arm interiors. It complements filter cleaning rather than replacing it.
White vinegar or citric acid does much the same job for a fraction of the price. A cup of vinegar in the empty machine on the hottest cycle is the traditional version and works well in hard water areas.
If the filter is damaged or the mesh is torn, replacement filters are inexpensive and readily available by model number. Running a machine with a damaged filter risks the pump, which is a far bigger bill.
And for anyone who finds the whole business tedious, machines with a food macerator genuinely reduce the frequency of this job. It's a specification worth looking for at purchase if maintenance is something you know you won't keep up with.
Frequently Asked Questions
How often should you clean a dishwasher filter?
Weekly if you don't scrape plates, fortnightly for typical use, monthly if you scrape thoroughly. Always after a load with rice, pasta or seeds.
Where is the filter in a dishwasher?
At the bottom of the tub, beneath the lower spray arm. Usually a cylinder that twists out, sitting in a flat mesh plate.
Do modern dishwashers have self-cleaning filters?
Some have food macerators that grind waste. They still need periodic checking, since grease accumulates on the surrounding mesh.
Why is my dishwasher leaving grit on the dishes?
Almost always a blocked filter. The wash water is recirculated, so a clogged filter means dirty water is being sprayed back onto the load.
Should I rinse plates before loading?
Scrape, don't rinse. Auto programmes measure soil level, and a thoroughly rinsed load triggers a weaker cycle.
Can a blocked filter damage the dishwasher?
It reduces spray pressure and can let debris reach the pump if the filter is damaged or badly refitted. The pump is the expensive part.
Final Thoughts
This is the highest-value two minutes available to a dishwasher owner, and the reason it gets skipped is that nothing prompts you to do it. There's no light, no beep, and the decline is slow enough to look like age.
Attach it to something you already do — topping up the rinse aid, or the first wash of the month — and it stops being a job you forget. Most complaints about dishwashers not cleaning properly are solved by it entirely.
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