Check these, in this order
The order matters. It runs from the cause that is most common and costs nothing to the one that is rare and costs money.
Step 1. Stop pre-rinsing the dishes
This feels backwards and it is the single most common cause. Modern detergent contains enzymes that need food residue to work against. Give them a spotless plate and they have nothing to grip, so they leave a film behind instead. Scrape solids into the bin, and put the rest in dirty.
Step 2. Clean the filter
A blocked filter recirculates dirty water over your dishes for the whole cycle. Twist the filter assembly out of the tub floor, separate the mesh from the cylinder, rinse both in hot water and brush the mesh. Monthly is enough to keep this from ever being the cause.
Step 3. Clear the spray arm holes
Take the arms off, usually a clip or a nut in the centre, and hold each one up to the light. Every hole should be open. Hard water blocks them with limescale and label fragments block them outright. A toothpick or a piece of wire clears them, then rinse the arm through from the centre.
Step 4. Spin the arms by hand and watch what stops them
With the racks loaded as you normally load them, turn each arm through a full circle. If a handle, a baking tray or a tall glass catches it, that section of the machine gets no water at all. This is why a poorly loaded machine cleans the front but not the back.
Step 5. Check how hot the water arrives
A dishwasher needs water at about 120F to dissolve grease and activate detergent. Run the kitchen tap hot for a minute before starting a cycle: if it never gets properly hot, the machine starts every wash with cold water. Where the water heater is set below 120F, raising it fixes the dishwasher. Do not go above 140F, which is a scald risk at the tap.
Step 6. Use rinse aid, and check the salt if your machine takes it
Rinse aid is not a luxury item: it breaks the surface tension so water sheets off rather than drying into spots. In hard water areas a machine with a softener also needs its salt topped up, and running it empty leaves white film on everything.
Step 7. Run a hot cycle with a machine cleaner
If the film is on the inside of the machine as well as the dishes, there is grease and limescale through the whole spray system. A proper dishwasher cleaner at the highest temperature strips it. Repeat every few months in hard water.
What a technician will look at next
Check the circulation pump
If the filter is clean, the arms are clear and spin freely, the water is hot and the machine still leaves food on the dishes, the circulation pump is not producing pressure. That is a repair rather than a habit.
When to stop and call someone
Only after all of the above. The order matters: seven of these eight checks cost nothing, and a technician will start by asking whether you have done them. If you can say yes to all of them, the visit is worth booking.
What it costs
| Repair | Part only | Fitted by a technician |
|---|---|---|
| Loading habits, filter, spray arms, rinse aid | - | Free |
| Dishwasher cleaner and rinse aid | - | $10 to $25 |
| Circulation pump replacement | - | $200 to $450 |
If a code is showing too
Questions people ask
- White gritty film on everything. Is that detergent or hard water?
- Almost always hard water. Add rinse aid, top up the softener salt if your machine has a compartment for it, and run a cleaner through it. If the film wipes off with vinegar on a cloth, that confirms limescale.
- The top rack is clean and the bottom is not, or the other way round.
- That points at one spray arm rather than the whole machine. Take that arm off and check every hole is open, then check nothing in the rack blocks it as it turns.
- Does it matter which detergent I use?
- More than people expect. Tablets with built-in rinse aid work well in soft water and underperform in hard water, where separate rinse aid and salt do better. Powder lets you use less on light loads, which also helps if you have had foam problems.
- Should I run the hot tap before starting the dishwasher?
- It genuinely helps if the machine is far from the water heater. The first fill otherwise draws whatever cooled in the pipe, and the machine spends part of the cycle heating it instead of washing.