Dishwasher Not Cleaning Dishes? 7 Causes, From Spray Arms to Pumps

A dishwasher that runs its full cycle and hands you back gritty glasses and plates with yesterday’s dinner still attached is doing the worst kind of failing: using all the water and power, delivering none of the result.

The encouraging news is that a dishwasher not cleaning properly usually is not broken in the expensive sense. Most of the causes are blockages and habits, fixable this afternoon, and the genuinely mechanical causes announce themselves clearly once you know what to look for.

Work through these seven in order. They run from most to least likely, and the first four need no tools at all.

1. Blocked spray arms

Every jet of water your dishes get comes from the small holes in the spray arms, and those holes block with food fragments, seeds, glass chips and hard-water scale. A few blocked jets means whole zones of the load get missed, which is why the top rack often suffers first.

Pull the arms off, most twist or clip free, hold them up to the light, and poke each blocked hole clear with a toothpick or skewer. Rinse them through under the tap, spin them by hand as you refit them, and make sure nothing tall in the racks stops them rotating freely. A spray arm that cannot spin cleans exactly one stripe of the load.

2. A filthy filter recirculating dirty water

Your dishwasher washes with the same water it just rinsed off the plates, filtered and recirculated. When the filter mats over with grease and food, the machine effectively paints your dishes with dirty water, and grit on glasses is the classic signature.

Twist out the filter in the floor of the tub, rinse it under a hot tap and scrub the mesh with an old brush. If this is new territory, our guide to a dishwasher that will not drain covers the same filter, because a blocked one causes both problems. Monthly is the right cleaning rhythm.

3. Loading that blocks the water

Water travels in straight lines. A chopping board leaned across the bottom rack, pots nested together, or a platter shadowing the detergent dispenser will beat any dishwasher ever made.

Face the dirty side of everything toward the spray, keep tall items to the sides and back, do not nest bowls, and leave the dispenser’s line of fire clear. And scrape plates rather than rinsing them spotless: modern detergent enzymes need some soil to work on, and pre-rinsed loads can actually come out worse.

4. Detergent, rinse aid and salt

Old detergent absorbs moisture and loses its punch, cheap tablets sometimes fail to dissolve fully, and a dispenser crusted with residue may not open on cue. Check the dispenser flips open freely and comes out empty at cycle end.

Rinse aid is not optional on modern machines: without it, water dries in droplets and leaves film and spots, which reads as poor cleaning. Top it up. If you are in a hard-water pocket and your machine has a salt reservoir, keep it filled, because scale quietly degrades everything downstream.

5. Water not getting hot enough

Detergent chemistry is built around hot water. If the machine’s heater element is failing, cycles run cool, grease stops dissolving, and tablets can come out half-melted. A cycle that finishes with the door and dishes barely warm, on a machine that used to steam when opened, points this way.

A failed heating element is a proper fault, technician territory, and one of the most common repairs we do on machines that clean poorly but drain fine.

6. A tired wash pump or worn seals

The wash pump provides the pressure behind every jet. As it wears, or as its seals and housings leak pressure internally, spray gets weaker across the whole load, and cleaning declines gradually over months rather than overnight.

The pattern that gives it away: filter clean, arms clear, water hot, loading sensible, and results still mediocre and slowly worsening. That is a pressure problem, and it needs a technician’s diagnosis rather than another bottle of dishwasher cleaner.

7. Inlet and water-supply problems

A partly closed isolation tap, a kinked inlet hose or a clogging inlet valve starves the machine of water, so it washes with less than a full charge. Some machines show an error code for it, many just clean badly.

Check the tap under the sink is fully open and the hose has a clear run. Beyond that, inlet valves are cheap parts a technician swaps quickly.

If you have worked the whole list and your dishwasher is still not cleaning well, it has earned a professional look. CAI Appliance Services has repaired dishwashers across Perth for over 25 years, and we are the authorised service agent for several major brands including Bosch, Miele, Asko and Dishlex. Details on our dishwasher repair page.

Dishwasher not cleaning: the quick version

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