Dishwasher Not Cleaning: Film, Grit and What Causes Each

A dishwasher that stopped cleaning properly is rarely one broken part. It is more often several small things that have each drifted a little, and around San Diego one of those is nearly always the water, which is hard enough to leave a mark on glassware on its own. Work through it in the order below and most machines come back without a part being fitted.

Separate the film from the grit before diagnosing

These look similar in a cupboard and are unrelated.

Film is even. It coats glasses, the inside of the door and the racks alike, it looks cloudy or chalky, and it is the same after every wash. That is mineral scale and detergent residue, and it comes from water hardness, too little rinse aid, or too much detergent for the load.

Grit is uneven. Specks and particles land on some items and not others, often on upward-facing surfaces and inside cups, and there is usually food debris involved. That is soil the machine picked up and put back down, which means it is not filtering, not draining or not spraying properly.

A quick test for film: soak one clouded glass in white vinegar for a few minutes. If it clears, it is mineral scale. If it stays cloudy, the glass is permanently etched, which is a different problem and not repairable.

The filter, and why older machines did not need this

Most dishwashers sold in the last fifteen years or so have a manual filter in the floor of the tub: a flat coarse screen and a fine cylinder that twists out of the middle. It is quiet, it is efficient, and it needs cleaning by hand. Older machines had a hard-food disposer that ground debris up instead, which is why people who kept one for years never had to think about it.

A blocked filter means the wash water is being pumped through a layer of trapped soil, which is exactly the grit that ends up back on the dishes.

• Pull the bottom rack out and twist the fine filter anticlockwise to release it.
• Lift out the coarse screen underneath.
• Rinse both under a hot tap with a soft brush, particularly the fine mesh, which clogs with fat rather than solids.
• Wipe the recess they sit in, and look for glass chips or a fruit sticker in the sump.
• Refit and turn until it locks. A filter left unlocked lets debris straight into the pump.

Once a week is right for a busy household, once a month for a light one.

Spray arms: whether they turn, and whether the holes are open

Everything the machine does depends on water reaching the dishes at pressure. Two things stop that, and both are visible in a minute.

Spin each arm by hand. It should turn freely through a full circle without touching anything. The most common single cause of a poor wash is a tall item, a handle, a chopping board or a pan, blocking the arm before the cycle even starts.

Then look at the holes. Hard water blocks the outer holes first, because they do the most work, and a machine with a scaled outer ring cleans the middle of the rack and misses the edges.

• Take the lower arm off, usually a clip or a single nut, and the upper arm the same way.
• Clear each hole from the outside with a wooden toothpick or a short length of wire.
• Rinse the arm out under the tap to flush what you pushed in.
• Check the feed at the back for the upper arm, and on machines with a ceiling jet check that too.

Water arriving too cool defeats the detergent

Dishwasher detergent works chemically, and its enzymes and bleaching agents need the water hot to do anything. Cool water gives a wash that looks like a mechanical fault and is not one.

Run the kitchen tap until it is properly hot before starting the machine. In a condo, and in older buildings where the water heater is a long way from the kitchen, the first fill would otherwise be the cold water sitting in the pipe run, and some cycles never recover from that.

Around 120F at the tap is the usual recommendation. Beyond the supply, the machine has its own heating element and a thermistor telling the control what the temperature is. A failed element gives a machine that washes poorly and also leaves everything wet at the end, since the same element usually drives the dry. That combination is a strong clue.

Skipping the eco or short programme is worth trying too. Those cycles save energy largely by using less heat and less time, which is exactly what a machine struggling to clean does not have to spare.

Hard water is the local factor, and rinse aid is not optional

San Diego water is imported and hard, and hardness is the direct cause of the white haze on glassware. It also scales the element, the spray arm holes and the internal pipework slowly, so it makes every other fault on this page arrive sooner.

Rinse aid is misunderstood. It does not clean anything. It lowers the surface tension so the final rinse sheets off the dishes instead of beading, and the mineral in those beads is what dries into spots. Keep the reservoir filled and turn the dosage setting up if you still see spotting.

If the machine has a built-in water softener with a salt reservoir, which many Bosch and Miele models do, use it and set it for hard water. That is the single most effective thing available on those machines and it is frequently left switched off.

For existing scale, run an empty hot cycle with a citric-acid dishwasher cleaner. Do not use chlorine bleach in a stainless tub.

Detergent: how much, how old and whether it got out

Detergent that never reached the wash cannot clean.

• Check the dispenser door is not blocked. A tall plate or a baking tray in the front of the lower rack holds it shut, and everything after that is a rinse in warm water.
• Powder and tablets lose strength with age and with humidity. A box open for a year in a coastal kitchen is not what it was. Buy smaller quantities.
• Tablets need the main dispenser, not thrown in the bottom of the tub, where they dissolve during the prewash and are pumped out before the main wash starts.
• If the machine has a small prewash chamber or a lip beside the main cup, a little detergent there helps on heavily soiled loads.
• Overdosing does not clean better. On soft or medium loads it leaves the residue that shows up as film.

Loading changes the result more than people expect

Modern detergents are built around enzymes that need something to work on, so scraping is right and rinsing dishes until they are already clean actually makes the wash worse.

• Scrape solids off, leave the rest.
• Face soiled surfaces inwards and downwards, towards the spray arms in the centre.
• Do not nest bowls or spoons; anything sheltering another item leaves both dirty.
• Angle bowls and cups so water runs off rather than collecting.
• Keep plastics on the top rack, away from the element.
• Leave space. An overfilled machine is the commonest reason a perfectly good dishwasher appears to have failed, and in a small kitchen with one load a day the temptation to cram it is constant.

When it is a fault and not a habit

If the filter is clean, the arms turn freely with open holes, the water is hot and the loading is sensible, and it still comes out dirty, then it is the machine.

• Water standing in the bottom at the end means it is not draining, so the main wash is running in the last load's dirty water. Check the filter and sump first, then the drain hose and the disposal connection, which is very often the cause when a garbage disposal was fitted recently and the knockout plug was left in.
• Only the top rack coming out dirty usually means the upper feed or the diverter valve, which alternates water between the arms and can fail leaving one starved.
• A wash that sounds much quieter than it used to often means the circulation pump is weak or the chopper has failed.
• A machine that never quite fills gives the same poor result, and that points at the inlet valve or a partly blocked supply.

Take a note of which of these it is before anyone opens the machine. The symptom pattern narrows it far more than a general complaint that it is not cleaning.

What you can check yourself

1. Decide whether you are looking at even film or uneven grit; they have different causes.
2. Twist out and rinse both filters, weekly in a busy household.
3. Spin both spray arms by hand and clear any blocked holes from the outside.
4. Run the kitchen tap hot before starting a cycle.
5. Keep the rinse aid reservoir filled, and use the salt softener if the machine has one.
6. Check the detergent dispenser door is not blocked by a tall item in the lower rack.
7. Scrape rather than rinse, and stop nesting bowls and cutlery.
8. Check for standing water at the end of a cycle, which means a drainage fault.