The short answer
Poor washing on a full-size machine is nearly always the filter, the spray arms or the loading rather than the pump. Pull the filter and spin both arms by hand: those two checks take five minutes and resolve the great majority of complaints.
What you actually see and hear
- Grit redeposited over the whole load — The filter is full and the machine is washing with dirty water.
- Clean at the bottom, dirty at the top, or the reverse — One spray arm is not getting water or not turning.
- Greasy film, worst on plastics — Wash temperature or detergent rather than mechanics.
- Dried food only on items that were nested or face-up — Loading. Water cannot reach a surface it cannot see.
- NEAR MISS - chalky white residue on glass — Hardness and rinse aid. A different complaint entirely.
Causes, most likely first on this machine
- Filter and sump full — First. It is designed to be cleaned regularly and almost never is, and once it is loaded the machine circulates the soil rather than removing it.
- Spray arm blocked, plugged or not turning — Second. A tall item through the upper rack, or jets plugged with seeds and labels, removes whole sectors of the load from the wash.
- Loading errors and overloading — Third, and it is the cause most owners resist: nested bowls and overlapping plates shield each other completely.
- Water temperature at the machine — Fourth. A long cold supply run means the machine starts cold, and on a short cycle it never catches up.
- Detergent type, dose and rinse aid — Fifth. Old or damp detergent and an empty rinse aid reservoir both show up as poor results.
- Wash pump or diverter — Last. A genuine fault, but it leaves everything dirty rather than leaving a pattern.
Check in this order, and why
- Pull the filter and look at it — If it is loaded, clean it and run the machine again before doing anything else.
- Spin both spray arms by hand with the racks in — Anything they touch is a sector that will not be washed.
- Hold each arm up to the light and check the jets — Plugged jets map directly onto the pattern of dirty items.
- Run the hot tap at the sink before starting a cycle — It removes the cold slug from the supply line and costs nothing.
What an owner can safely check
- Remove and rinse the filter, and wipe the sump — Wear a glove - glass chips collect here.
Tools: gloves, warm water, brushAbout 15 min
- Spin both spray arms and remove whatever blocks them — Tall items in the upper rack are the usual obstruction.
About 5 min
- Clear the spray jets with a cocktail stick — Go round every hole against the light.
Tools: cocktail stickAbout 15 min
- Run the hot tap at the sink until it runs hot, then start the cycle — A simple habit that improves results on most installations.
About 5 min
- Run a hot empty cycle with a dishwasher cleaner — Removes the grease and scale film that dulls results everywhere.
Tools: dishwasher cleanerAbout 90 min
- STOP HERE before removing the sump or the wash pump — That is service work in a wet cabinet.
Before you open anything
Safety
Unplug the appliance or switch off its breaker before removing any panel - a capacitor can hold a charge after the power is off. A dishwasher sits in a wet cabinet with a live connection behind it, so switch off at the breaker before pulling it out, and close the isolating valve under the sink before touching a hose. Let a hot cycle cool before reaching into the tub.
When to call a technician
Call when the filter is clean, both arms spin and spray freely, the load is sensible, the supply is hot and results are still poor - that points at the wash pump, the diverter or the heater. Mention whether the machine still gets hot during a cycle, because a machine that washes cold will wash badly with every mechanical part in perfect order. For chalky marks and cloudy glass, do not call: that is water hardness and rinse aid.
Nearest pages of this class
What this page does not cover
This page is written for the full-size tall-tub dishwasher class, not for one family or model line. Where a brand- or model-specific page exists for your unit it is the more specific answer and it is linked above, so go there first if your machine is named. What is deliberately not here: spray arm and pump part numbers, chopper blade specifications, hose routing diagrams and control diagnostics, all of which differ by family and belong on the page for that family.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
