The short answer
A Costway dishwasher that leaves dishes dirty is usually recirculating debris, missing part of the load with its spray, or washing too cool for the detergent to work. On this class the usual cause is a tap connection giving less flow and heat than the cycle needs, with a load blocking the arms or shielding itself next to rule out.
What you actually observe
- Results vary from wash to wash with no pattern — A connection that is reseated for every cycle varies with it.
- Results have fallen off gradually over months — Gradual decline is scale or a filter rather than a failure.
- NEAR MISS: the machine finishes with water still in the bottom — That is a drainage failure and it has its own page and cause list.
The causes, most likely first on this brand
- A tap connection giving less flow and heat than the cycle needs — Ranked first on a Costway unit: this class draws everything through an adaptor on the kitchen tap, so the fill is only as good as that connection and it is the first thing to check.
- A load blocking the arms or shielding itself — Bowls nested together, large pans laid flat and tall items across the upper basket all stop the water reaching everything behind them, and the machine gets the blame. Ranked second here: a compact tub is easily overloaded and its single arm is easily blocked.
- Detergent that is old, wrong or badly dosed — Ranked third here: a small machine needs a smaller dose than the box suggests.
- Spray arm holes blocked or an arm that cannot turn — Ranked fourth here: last, though a single arm doing all the work silts up sooner.
Check in this order, and why this order
- Watch the adaptor while the machine fills and check the tap is set to hot — A trickle or a lukewarm fill explains poor results before anything else is suspected.
- Spin both arms by hand with the machine loaded as usual — Anything the arm touches is stopping the wash for everything downstream of it.
- Check how old the detergent is and how it has been stored — A box opened last year in a cupboard beside the machine is a real cause and a common one.
What an owner can safely check
- Seat the adaptor squarely, open the tap fully and set it to hot before starting — This class of machine depends entirely on the connection being right.
About 10 min
- Reload so nothing blocks the arms, nothing nests and every soiled face points at a spray arm — Fewer items loaded properly beats more items loaded badly every time.
About 15 min
- STOP HERE if the next step needs a meter on live terminals or a panel off — That is where an owner check ends and a service call begins.
Before you open anything
Safety
Switch the machine off at its breaker before reaching into the sump or removing any part, because the heating element in the floor of the tub stays hot for a long time after a cycle. Never put hand dishwashing liquid into a dishwasher, and never mix a descaler with bleach or with any other cleaning product. Open the door carefully at the end of a cycle, because the steam that comes out will scald.
When to call a technician
Call once the filter, the arms, the load, the detergent and the fill are all clean and the results are still poor, because a wash pump or a heater needs the machine pulled and a meter. Call sooner if the tub is not heating at all, since a cold wash on every cycle points at one component. Bear in mind when you decide that parts for a value import are not stocked locally and a replacement unit can cost less than a part plus a labour call.
Nearest pages of this class
What this page does not cover
This page covers the Costway dishwasher as a class, not one family or model line. Filter designs, cycle structures and detergent dosing all change from build to build and are deliberately not here. Where a family or model page exists for your machine, it is the more specific answer and the one to read first.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
