Discover easy fixes for a dishwasher not cleaning properly. Learn how to check filters, spray arms, limescale, detergent and loading to improve cleaning.
You've run a full cycle, the machine has beeped, and you open the door expecting clean crockery. Instead, you find greasy glasses, food still stuck to the plates, and a faint smell that suggests nothing much happened in there at all. It's one of those household frustrations that feels disproportionately annoying, mainly because a dishwasher not cleaning properly is usually down to one of a handful of fixable causes once you know where to look.
Blocked filters and clogged spray arms are among the most common causes of poor dishwasher cleaning. That's not a coincidence: these are maintenance issues rather than mechanical failures, and they're often fixable at home without any parts at all. This article walks through the most likely causes in the order you should check them, explains the fixes clearly, and tells you when the problem has moved beyond DIY territory.
Most cleaning failures have nothing to do with a broken dishwasher. A clogged filter, blocked spray arm jets, limescale build-up, poor detergent choice, and overloading account for the overwhelming majority of cases where dishes come out dirty after a full cycle. Working through these in the right order takes less than an hour and, in most cases, solves the problem completely.
Start with the filter, which sits at the bottom of the tub and collects food debris over time. A clogged filter restricts water circulation, meaning dirty water gets recirculated over your dishes rather than draining away cleanly. Next, check the spray arms: if the small jets are blocked with mineral deposits or food particles, water simply won't reach
every surface in the machine.
Hard water is the third issue, and it's a significant one across London and the South of England. Limescale coats the heating element and spray holes, reducing both temperature and spray pressure over time. The fourth culprit is detergent: the wrong type for your water hardness, or tablets that aren't dissolving fully, will leave dishes dirty regardless of how clean the machine itself is. Finally, overloading is the most overlooked cause of all. When dishes are stacked too tightly or tall items block the spray arms, water and detergent can't do their job.
The filter assembly sits at the base of the dishwasher tub, usually beneath the lower spray arm. You're looking for a cylindrical mesh component that twists out of the floor of the machine. Signs it needs attention include a gritty residue on plates after a cycle, a stale or musty smell when you open the door, and water sitting at the bottom of the tub after the cycle ends. Most manufacturers recommend inspecting it monthly and cleaning it every one to three months if the machine is used frequently, otherwise roughly every three to six months. Check your own manufacturer's guidance, as recommendations vary by brand and model.
Here's how to do it:
That last step matters more than most people realise. A filter that isn't locked securely will allow debris to bypass it entirely, and the problem is likely to return quickly. Take a second to confirm it's properly seated before replacing the rack.
Both the lower and upper spray arms can be removed on most dishwashers. The lower arm typically lifts straight off its mount, while the upper arm usually unscrews or twists free from a locking ring beneath it. Once removed, hold each arm up to a light source and look through the spray holes. Any that appear blocked or reduced in size need clearing.
Use a cocktail stick, toothpick, or thin wire to clear each hole individually, working from the outside inward. Rinse the arm under warm running water to flush out whatever you've loosened. For stubborn mineral deposits, soak the arm in a bowl of warm water and white vinegar for 15 to 30 minutes before rinsing again. White vinegar works well as a mild descaling option; for heavier build-up, a citric-acid-based dishwasher descaler is worth considering instead.
After refitting each arm, spin it by hand. It should rotate freely with no resistance and no rubbing against the rack or the mounting hub. Hold it up to the light one more time to confirm you can see clearly through each hole before you run another wash. If an arm still feels stiff after cleaning, the issue may be a cracked hub or a damaged bearing rather than a blockage. That's the point to stop and call an engineer: running cycles with a compromised spray arm won't fix the problem and can sometimes make the underlying fault worse.
Many parts of the UK have notably hard water, and London along with much of the South of England is classified as hard or very hard water territory. When hard water is heated inside the dishwasher, calcium and magnesium precipitate out and deposit as limescale on the heating element, spray holes, and internal pipes. Even a thin coating measurably reduces heating efficiency and spray pressure, which is why dishes gradually start coming out cloudy or with a chalky white film rather than failing suddenly.
If your machine has a built-in water softener, check that the salt reservoir is topped up. Dishwasher salt actively counters limescale formation and is one of the simplest maintenance steps you can take. You can check the exact water hardness for your postcode through your water supplier's website, which is worth doing so you can set the machine's hardness level correctly.
Powder detergents are often better suited to hard water areas because they typically contain water-softening agents and allow you to adjust the dose upward when the local supply is particularly hard. All-in-one tablets work well in most conditions, but they can underperform in very hard water unless the machine's hardness setting is correctly configured. If your tablets aren't dissolving fully after a cycle, check three things: whether the wash temperature is set correctly, whether the dispenser door opens freely during the cycle, and whether the machine is overloaded to the point where water circulation is restricted.
Run an empty hot cycle with a purpose-made dishwasher descaler every two months, or roughly every 60 cycles. White vinegar placed in the base of the machine works as a lighter option for general freshening between descales. Match your machine's water hardness setting to your actual local supply rather than leaving it on the factory default, many machines ship with a generic setting that may not suit your area. Most machines allow this adjustment through the settings menu, and it makes a noticeable difference to both cleaning performance and how quickly limescale builds up.
Overloading is the single most overlooked cause of a dishwasher not cleaning dishes thoroughly. When items overlap or tall objects block the spray arms from rotating, water and detergent simply can't reach every surface. Bowls and cups should always face downwards and inwards so water drains off rather than pooling. Large flat items such as chopping boards and baking trays belong on the sides of the lower rack, not across the front where they block the detergent dispenser door from opening during the cycle.
Cleaning the filter takes around five minutes once a month, though the exact time varies by model. Running an empty hot cycle with a descaler every couple of months is inexpensive (many products cost just a few pounds per treatment) and prevents the gradual build-up that causes most limescale-related faults. Checking that the salt and rinse aid reservoirs are topped up before a weekly wash adds 30 seconds to your routine. These small habits address the root causes of a dishwasher not cleaning properly before they develop into faults that require parts or a repair visit.
If you've cleaned the filter, cleared the spray arms, checked the detergent, topped up the salt, and adjusted the hardness setting, but dishes are still coming out dirty, the fault is likely internal. A heating element that no longer reaches the correct temperature, a faulty inlet valve restricting water flow, a detergent dispenser door that doesn't open during the wash cycle, or a failed circulation pump all produce the same symptom: poor cleaning that no amount of maintenance will resolve.
Three specific symptoms point clearly to an internal fault: the machine feels cool or only lukewarm when you open the door immediately after a cycle; the detergent tablet or powder is still sitting intact in the dispenser after a full wash; or dishes in certain parts of the machine consistently come out dirtier than others, suggesting the circulation pump isn't generating enough pressure.
These faults need a trained engineer with diagnostic equipment. Running more cycles hoping the problem resolves itself won't help and can sometimes cause secondary damage to other components.
For homeowners across London and the South of England, Alpha Appliances Ltd offers fixed-price dishwasher repairs with no hidden call-out fees and no obligation to proceed until you've agreed to the quote. Engineers carry common replacement parts, which means most faults are diagnosed and resolved in a single visit. Appointments are usually available the next working day across Greater London and much of the South, a practical option when DIY troubleshooting has reached its limit and you need the job done properly.
Work through the checks in this order: clean the filter first, then clear the spray arms, then address water hardness and detergent choice, then review how you're loading the machine. The majority of cases where a dishwasher isn't cleaning properly are resolved at one of these five steps, without spending anything on parts, just time and a soft brush.
If the machine still isn't performing after all of those checks, the fault almost certainly lies with a component rather than a maintenance issue. A heating element, dispenser mechanism, circulation pump, or inlet valve fault won't respond to cleaning, but it will respond to a proper diagnosis from a qualified engineer. That's a manageable repair in the right hands, and it's usually considerably cheaper than buying a replacement machine.
If your dishwasher is not cleaning after working through these steps, the team at Alpha Appliances is available to book online or by phone, with appointments available across the region as early as the next working day.
The most common reasons are a blocked filter, clogged spray arm jets, limescale build-up, or a detergent issue. Work through each cause in the order described above before assuming a mechanical fault.
Inspect it monthly and clean it every one to three months if the machine runs frequently. If you use it less often, cleaning every three to six months is usually sufficient. Check your manufacturer's handbook for model-specific guidance.
Yes. Limescale from hard water reduces spray pressure and heating efficiency over time. Keeping the salt reservoir topped up, matching the machine's hardness setting to your local supply, and running a descaler cycle every couple of months all help to prevent this.
If you've worked through all the maintenance checks, filter, spray arms, salt, detergent, loading, and dishes are still coming out dirty, the fault is likely internal. A qualified engineer can diagnose heating element, pump, or dispenser faults quickly and resolve most issues in a single visit.
Book a visit from a certified Alpha engineer in minutes.
TRUSTED BY HOMEOWNERS
Fast, reliable, and warranty-backed repairs for every major brand.
Discover more tips from Alpha engineers.
