Most dishwasher faults trace back to three things: the filter, the spray arms, or the door seal — not the pump, the motor or the control board. A blocked filter alone accounts for a large share of the water-left-behind and not-cleaning complaints people bring to an engineer. Fifteen minutes of cleaning solves more dishwasher problems than any part you could order.
How a wash cycle actually works
Knowing the sequence makes it much easier to place a fault, because the machine fails at a specific stage and the stage tells you where to look.
- Fills
A measured amount of water enters through the inlet valve — not a full tub, just enough to cover the base.
- Heats and washes
Water is drawn up through the filter, pumped to the spray arms, and blasted around the tub. It then drains straight back through the filter to be reused for the next spray, over and over during the cycle.
- Drains between phases
Dirty water is pumped out and fresh water brought in for the rinse phases. This is where a blocked filter or pump causes the most visible symptom: standing water at the end of the cycle.
- Rinses and rinse-aids
A final clean rinse, with rinse aid dosed in to help water sheet off rather than form droplets that dry into spots.
- Dries
Either a heating element, residual heat, or a fan finishes the job depending on the model.
The key insight: water is recirculated through the filter constantly during the wash, not just at the end. A partially blocked filter does not just leave water behind — it starves the spray arms of clean water throughout the whole cycle, which is why a dirty filter causes both drainage complaints and cleaning complaints at once.
Find your fault by symptom
| Symptom | Most likely cause | Full guide |
|---|---|---|
| Water left in the bottom | Blocked filter, drain hose or garbage disposal knockout | Dishwasher not draining |
| Dishes come out still dirty | Blocked filter or spray arm holes, or overloading | Dishwasher not cleaning |
| Will not start at all | Door latch, child lock, or delay setting | Dishwasher will not start |
| Water pooling under the door | Worn door seal or gasket | Dishwasher leaking from the door |
| E15 code / water in the base tray | Anti-flood float triggered by an internal leak | Bosch E15 error |
| White film on glasses | Hard water, or rinse aid empty | See our white film guide |
| Bad smell | Trapped food debris, or a drain problem, not the machine itself | See our smell guide |
| Dishes come out wet | Rinse aid empty, low temperature setting, or a failed heating element | See our not-drying guide |
The three checks that solve most faults
Switch off at the wall before removing the filter assembly or reaching near the spray arm mounts. If the machine has just run, let the water cool — it is hotter than it looks.
- Clean the filter assembly properly
Almost every dishwasher has a removable filter at the bottom of the tub — usually a coarse outer mesh and a fine inner cylinder that twist apart. Take both out, rinse under a hot tap, and scrub off the greasy film with an old toothbrush. Do this monthly. A filter that looks merely damp rather than visibly clogged can still be restricting flow enough to cause problems.
- Clear the spray arm holes
Lift each spray arm out and hold it up to the light. The small jets block with limescale and food debris over time. Poke each one clear with a toothpick or a piece of stiff wire, and check the arms spin freely once refitted — a knife or a large item leaning against one is a common, completely avoidable cause of poor cleaning.
- Check the door seal
Run a finger around the full length of the rubber gasket. Look for splits, food debris holding a section open, or a part that has come out of its channel. This is the main cause of leaks at the door, and unlike most dishwasher faults it is not connected to the filter or spray arms at all.
A maintenance cycle on the hottest setting, empty, with either a proprietary dishwasher cleaner or a bowl of white vinegar placed upright on the top rack, clears grease and limescale that ordinary washes leave behind. This single habit prevents a large share of smell and cleaning complaints before they start.
Water quality matters more than people think
Two water-related issues get blamed on the machine constantly:
- Hard water causes white spotting and film, and it also accelerates limescale build-up inside the spray arms and heating element. Using the right amount of dishwasher salt (on machines with a softener) and rinse aid matters more in hard water areas than the detergent brand does.
- Low water pressure or temperature to the machine reduces cleaning performance across the board. Confirm the machine is on a hot feed if it expects one, and that the inlet valve is opening fully.
Repair or replace?
Cheap and worth doing at almost any age: filters, spray arms, door seals, drain hoses, inlet valves, and — on most brands — heating elements. Expensive and worth thinking hard about: the wash pump assembly, the control board, and anything requiring the tub to be removed. On a machine past roughly eight to ten years, a major component failure is usually the point where a new machine — which will also run more efficiently — makes more sense than the repair bill.
When to call a professional
Call an engineer if the machine trips the breaker, if you find a leak that is not the door seal (which usually means the sump or tub — see our Bosch E15 leak error guide for how to trace it), if the pump runs but nothing moves through the spray arms after cleaning, or if a repair means removing the tub or replacing the control board. Anything involving the machine’s electrical or water inlet components sits next to live wiring and a pressurised supply.
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.
