You unload the dishwasher and find grit on the glasses, food stuck on the plates, or a white film across everything. It is frustrating, and most people assume the machine has given up. Often it has not. A dishwasher relies on a few simple things working together: clean water reaching the spray arms, detergent that dissolves, and a filter that is not clogged.
Here is how to work through it in a sensible order.
How a dishwasher cleans
The machine fills with a little water, heats it, and pumps it through spinning spray arms. The water falls back to the bottom, passes through a filter and is pumped around again. Detergent loosens the food, and the water carries it to the filter or the drain.
If the filter is clogged, the arms are blocked, or the water is not hot enough, food is just washed around and put back on your dishes. That is why gritty dishes are such a common complaint.
Safe checks to work through
- Clean the filter Most dishwashers have a filter at the bottom of the tub. Many twist out by hand, so check the manual. Rinse it under the tap and scrub gently with a soft brush. Put it back until it locks. A filter coated in grease and food scraps is the most common cause of gritty dishes.
- Check the spray arms Spin each arm by hand. It should turn freely. Look at the small holes along the arm. If they are blocked with food, seeds or hard water scale, clear them with a toothpick. Many arms lift or unscrew off for cleaning.
- Look at how you load Tall items can block the spray arm. Plates packed tightly together shield each other from the water. Face the dirtiest surfaces towards the centre and keep large items from covering smaller ones.
- Check the detergent Old tablets and powder can go lumpy or lose strength in a humid kitchen. Use fresh detergent. Make sure the dispenser door opens fully and is not blocked by a dish or a pot handle.
- Check rinse aid Top up the rinse aid reservoir if it is empty. Rinse aid helps water run off the dishes, so spots and film are much less likely.
- Try a hot, empty cycle Run the hottest cycle with nothing inside, and with a dishwasher cleaner if you have one. This helps clear grease and scale from the pump and spray arms.
Switch the dishwasher off at the wall before you remove the filter or spray arms, and do not open any panel. Everything on this list can be done with the tub door open and the power off.
What the dishes are telling you
- Gritty or sandy residue: a clogged filter, or a drain that is not clearing properly.
- Food stuck on plates: blocked spray arms, poor loading, or water that is not reaching the dishes with enough force.
- White cloudy film on glasses: hard water or too much detergent. Rinse aid and a lower dose can help.
- Greasy or oily feel: water that is not hot enough, or detergent that has lost strength.
- Dishes still wet at the end: a rinse aid or heating problem, which is a separate issue from cleaning.
Water temperature and inlet
Detergent works best in hot water. Most dishwashers heat their own water, but some pull in hot water from the house supply. If the machine fills slowly or with very little water, the inlet valve or its screen filter may be blocked. That is a job for a technician, because it means working on the water supply behind the machine.
Standing water
Look inside after a cycle. A shallow film of water around the filter is normal. If you see a pool of dirty water sitting in the base, the machine is not draining properly. Check the filter again and look for a kink in the drain hose under the sink. If the drain hose connects to the sink waste, see whether the sink drains freely too.
When it is a part
If the filter is clean, the arms spin freely, the detergent is fresh and the dishes are still dirty, a part may be failing. The common ones:
- Circulation pump, which pushes water to the spray arms. A weak pump means weak spray.
- Drain pump, which clears dirty water.
- Heating element or thermostat, when the water never gets properly hot.
- Inlet valve, when the machine takes in too little water.
- Detergent dispenser, when the door does not open at the right time.
- Control board or sensors on some models, when cycles end early or skip stages.
Many models from Miele, Bosch, Fisher & Paykel and Electrolux run a self cleaning or turbidity sensing cycle. A faulty sensor can make the machine think the water is cleaner than it is and shorten the wash. A technician can test this.
Keeping it working well
- Scrape plates, but there is no need to rinse them under the tap first. Modern sensors and detergents work better with some food present.
- Clean the filter every month or so.
- Use a dishwasher cleaner a few times a year.
- Check the spray arm holes whenever you clean the filter.
- Keep rinse aid topped up, especially if you have hard water.
If you have been through all of the above and your dishes still come out dirty, book Kobe. He repairs dishwashers across Brisbane's Northside and the Redlands, and he will test the pump, heater and dispenser to find out what is causing the problem before suggesting any parts.
Questions people ask
Why are my glasses cloudy after the dishwasher?
A white or milky film is usually hard water residue or too much detergent. Using rinse aid and a smaller dose often clears it. If the film wipes off with vinegar, it is mineral scale rather than etching.
Should I rinse dishes before loading the dishwasher?
Scrape off large scraps, but a full rinse is not needed. Many machines use sensors and detergent that work better with a little food on the plates.
How often should I clean the dishwasher filter?
About once a month for a busy household. It only takes a few minutes and is one of the most useful things you can do for clean dishes.