Why Your Dishwasher Isn't Cleaning Dishes Properly

Pulling out a load of plates that still have bits of last night's dinner stuck to them is frustrating, especially when you've waited an hour or more for the cycle to finish. The good news is that a dishwasher not cleaning dishes properly is one of the more solvable problems, and quite a few of the causes you can sort out yourself in a few minutes.

Below we'll walk through the usual reasons for poor washing results, how to tell them apart, and exactly what to do about each one. Some are simple maintenance jobs. Others point to a fault that needs an engineer, and we'll flag those clearly so you don't waste time.

How a dishwasher actually washes

It helps to understand what's going on inside. When the machine fills, it doesn't keep drawing in fresh water. It recirculates the same water for quite some time, pumping it up through the spray arms and firing it at your dishes again and again. Detergent, heat and that constant jet of water do the cleaning between them.

That recirculation is the root of a lot of poor washing complaints. If food hasn't been scraped off properly before loading, it ends up swirling around in that water. The motor then fires those food deposits out through the jets in the spray arms, and over time the jets clog up. Once that happens, the spray pattern weakens and your dishes don't get hit with enough water to come clean.

The most common causes of poor washing results

Work through these in order. They're roughly listed from the quickest checks to the ones more likely to need a repair.

1. Blocked spray arm jets

This is the big one, and the cause we see most often. Each spray arm has a row of small holes (jets) that direct water onto your dishes. Block enough of them and washing performance drops off a cliff.

There's one detail worth knowing. The two end jets on each spray arm are angled to make the arm spin. If one or both of those end jets are blocked, the arm stops turning altogether and sits static, so it can only spray one fixed spot instead of the whole load. That's a classic sign of blocked jets: clean dishes on one side of the rack, filthy ones on the other.

We've put the full cleaning procedure further down this page, because it's the fix that makes the biggest difference for most people.

2. A clogged filter

At the bottom of the dishwasher sits a filter that catches food debris so it doesn't keep getting recirculated. If it's caked in grease and scraps, the water can't flow freely and your dishes are being washed in dirty water.

Lift it out (most twist free), rinse it under a running tap, and use a soft brush to clear any trapped gunk. Make a habit of checking it regularly, especially if you don't rinse plates before loading.

3. The water isn't getting hot enough

Dishwashers rely on hot water to dissolve detergent and shift grease. If the water isn't heating, you'll typically see greasy films left on glasses and plates, and detergent residue that hasn't fully dissolved.

This usually comes down to a faulty heating element or a related component, and it isn't something you can put right yourself. If your dishes come out cold and greasy at the end of a cycle, it's worth booking an engineer to check the heating.

4. Overloading

It's tempting to cram everything in, but water and detergent need room to reach every surface. Overlapping plates, items nested inside each other and bowls blocking the spray arm all stop water getting where it needs to go.

Leave gaps, angle bowls and cups so water can drain off them, and make sure tall items aren't stopping the spray arms from spinning. Give the arms a gentle spin by hand after loading to check they turn freely.

5. The wrong detergent, or not enough of it

Old, damp or caked detergent doesn't dissolve properly. Hard water areas need more detergent than soft water areas, and tablets sometimes struggle on short or eco cycles because there isn't time for them to break down. If you've recently switched product or cycle and washing has got worse, that's a clue.

Check the rinse aid and salt levels too if your machine uses them. Low rinse aid leaves spots and streaks; low salt in a hard water area leaves a chalky film.

6. Food not scraped off beforehand

Going back to that recirculation point: the more solid food you put in, the more there is to block jets and filters. You don't need to pre-wash, but scraping plates into the bin first keeps the whole system cleaner and your results much better.

How to clean your dishwasher spray arms

If you're getting poor washing results, cleaning the spray arms is well worth the effort. It's straightforward and can make a significant difference to how well your machine performs.

Step 1: Remove the spray arms

Most dishwashers have two spray arms, one below the bottom basket and another below the top basket.

• The bottom spray arm is simply clipped into place. A small, firm pull lifts it free.
• The top spray arm usually sits on a screw thread. Turn it a quarter turn and pull it free.

Step 2: Clean each arm at the sink

Take each arm to the sink and run water through the central channel to check it's flowing freely.

Then, using something small and pointed like a pin or a needle, carefully pick each jet hole clear of blockages. This takes a bit of patience and persistence, but the aim is to get every hole completely clear, the two end jets especially, since those are what keep the arm spinning.

One important warning: do not try to make the jet holes any larger. Enlarging them changes the water pressure and will stop the arms spinning, which leaves you worse off than before.

Step 3: Refit the arms

• For the bottom arm, push it down until it clips back into place.
• For the top arm, attach it and turn a quarter turn in the opposite direction to lock it on.

Run a cycle and check whether washing has improved.

When it's time to call an engineer

If you've cleaned the spray arms and filter, sorted the loading and detergent, and you're still getting poor washing results, the cause is likely something internal that needs diagnosing properly. Common signs that point to a repair rather than maintenance include:

• Dishes coming out cold and greasy, suggesting a heating fault
• A spray arm that still won't turn even with clear jets
• Weak or no water circulation, which can indicate a pump or motor problem
• Dishes remaining dirty no matter what you try

We also repair dishwashers that won't close properly, leak or are making excessive noise. If any of that sounds familiar, our engineers can get to the bottom of it.

Before you do any hands-on checks of your own, it's worth reading how to safely isolate an appliance before a DIY repair.

Book a dishwasher repair with NAC

We repair every make of dishwasher, and our engineers are fully trained across all the brands we cover. You'll get a clear service charge quoted before anyone attends, covering all labour, callout and VAT where it applies. If parts are needed, we quote those separately first, so there are no surprises and no extra labour charges on top. Every repair comes with a guarantee, with the length depending on the parts fitted and covered by our terms and conditions.

If poor washing is getting you down, get in touch or call us on 0333 016 9622 to book a visit. You can also see the full range of appliances we repair and check we cover your area.

While you're sorting out the kitchen, you might also find our guide on common dishwasher drying problems useful for getting spotless, dry dishes every time.