Before suspecting a fault, rule out loading and habits — they cause more disappointing washes than any broken part. Beyond that, a blocked filter or clogged spray arm jets account for most genuine cleaning failures, because water is recirculated through both continuously during the wash, not just at the end.
Loading and habits worth ruling out first
- Overloading and nesting. Bowls stacked inside each other, or plates leaning against one another, block water from reaching the surfaces between them. Space items so water can reach every face.
- Blocking the spray arms. A tall item, a utensil poking through the rack, or a pan handle can stop an arm rotating entirely. Spin each arm by hand before starting a cycle if you are not sure.
- Pre-rinsing too thoroughly. Modern detergents are formulated to work on food residue — rinsing plates completely clean starves the enzymes of anything to react with and can actually make results worse. Scrape off solids; do not rinse spotless.
- Old or damp detergent. Detergent tablets and powder absorb moisture in a humid kitchen and lose effectiveness. Keep them sealed and check the use-by date.
Common causes
| Cause | How likely | Typical sign |
|---|---|---|
| Blocked filter assembly | Very common | Greasy film across all dishes, worst at the bottom |
| Clogged spray arm jets | Very common | Uneven cleaning — some items clean, others not |
| Spray arm obstructed or not spinning | Common | One area of the rack consistently dirty |
| Overloading | Common | Items facing each other or nested together |
| Water temperature too low | Common | Greasy residue rather than gritty film |
| Detergent dispenser blocked or wet | Occasional | Detergent tablet still sitting in its compartment at the end |
| Hard water without enough salt or rinse aid | Occasional | White film rather than actual dirt |
| Failed wash pump or impeller | Uncommon | Very weak spray from every arm, water level normal |
How to fix it
- Clean the filter assembly
Remove and rinse both the coarse and fine filters under a hot tap, scrubbing off any film with an old toothbrush. Because water recirculates through this filter throughout the wash, a partially blocked one starves the spray arms of clean water for the whole cycle — not just at the end.
- Clear every spray arm jet
Lift each arm out and check the small holes along its length. Poke each one clear with a toothpick or a strand of wire. Limescale and food debris both build up here gradually, so this is worth doing even if the arms look clean at a glance.
- Confirm the arms spin freely
Refit them and spin each by hand. They should turn smoothly with no resistance. If an arm catches, check nothing in the rack below it is fouling the rotation.
- Check the detergent dispenser
Make sure the flap opens fully and nothing in the top rack blocks it from swinging open. A dispenser lid stuck by an old detergent residue can fail to release the tablet at the right point in the cycle.
- Load with gaps, not stacks
Reload a test cycle with clear space around every item and nothing nested inside anything else. If this alone fixes it, the machine was never at fault.
- Run a hot maintenance cycle
Empty machine, hottest setting, a dishwasher cleaner or a bowl of white vinegar upright on the top rack. This clears the accumulated grease and scale that ordinary washes at lower temperatures leave behind, and often noticeably improves the very next full-load wash.
Water temperature and hardness
Cleaning performance depends heavily on hot water reaching the machine. If your dishwasher connects to the cold feed only and relies entirely on its own heater, cycles take longer and can under-perform on heavily soiled loads — check the manual for whether a hot feed is supported and worth connecting.
In hard water areas, a machine with a built-in softener needs dishwasher salt topped up regularly, separately from detergent. Skipping this causes exactly the kind of gritty white film that gets mistaken for poor cleaning, when the dishes are actually clean underneath the mineral deposit.
When to call a professional
Call an engineer if the filter and spray arms are clear, the load is well spaced, and cleaning is still consistently poor across every cycle — that points at the wash pump or its impeller not building enough pressure. Also call if water never seems to reach parts of the tub at all, which can indicate a pump or motor fault rather than a blockage.
Stop and call a qualified appliance technician or electrician if you find scorched or melted wiring, smell burning, see water that has reached electrical components, or if the fault returns immediately after a repair. Never bypass a safety device — thermal fuses, door interlocks and flood switches fail for a reason, and defeating one converts a broken appliance into a fire or flood risk.
