Quick answer: A dishwasher not cleaning properly usually has a clogged filter, blocked spray arm holes, poor loading, or water that isn’t hot enough. Cloudy or spotty glasses usually point to hard water, so use rinse aid and a detergent made for hard water. If the spray arms don’t spin, the dishwasher doesn’t fill properly, or dirty water stays in the bottom, a part has likely failed and needs a technician.
Opening the dishwasher to find food still stuck on plates is frustrating, especially when you’re counting on clean dishes for dinner. Most of the time, the fix is simple and takes only a few minutes. This guide covers 7 fixes to try, from easy checks you can do yourself to problems that need a repair, for homeowners in London, Woodstock, St. Thomas, and the surrounding area.
Dishwasher not cleaning? Common causes at a glance
| What you see | Most likely causes | Can you fix it yourself? |
|---|---|---|
| Food stuck on dishes | Dirty filter, blocked spray arms, overloading | Usually yes |
| Gritty residue on dishes | Dirty filter, drain problem | Clean the filter first |
| Cloudy glasses or white spots | Hard water, no rinse aid, too little detergent | Usually yes |
| Undissolved detergent | Blocked dispenser, cold water, low water fill | Check loading and water temperature first |
| Dirty water left in the bottom | Clogged filter, kinked drain hose, drain pump problem | Clean the filter; the pump needs a technician |
| Spray arms don’t spin | Blocked holes, items in the way, weak wash pump | Clean the arms; the pump needs a technician |
| Dishes cold and wet at the end | Heating element or thermostat failure | Needs a technician |
1. Clean the dishwasher filter
A clogged filter is the most common reason for a dishwasher not cleaning well. Food particles that can’t drain away get sprayed back onto your dishes, leaving a gritty film.
Most dishwashers made in the last 10 to 15 years have a manual filter that needs cleaning, usually once a month or more often if you run it daily. It’s located on the floor of the tub, under the lower spray arm. Twist it out, rinse it under hot running water, and scrub it gently with a soft brush. Check your manual if you’re not sure how yours comes out.
2. Clear the spray arms
The spray arms have small holes that can clog with food, seeds, or mineral scale. Remove the arms (most unclip or unscrew), rinse them, and clear each hole with a toothpick. Before starting a cycle, spin each arm by hand to make sure nothing is blocking it, like a pan handle or a utensil hanging through the rack.
If the arms are clean but still don’t spin during a cycle, the wash pump may be weak or failing. That needs a technician.
3. Load the dishwasher correctly
- Don’t overload it. Water needs space to reach every surface.
- Face dirty surfaces toward the centre and toward the spray.
- Put large pots and pans on the bottom, along the sides or back, so they don’t block the spray arms or the detergent dispenser.
- Keep bowls and cups from nesting inside each other.
- Scrape off food, but don’t pre-rinse. Modern detergents contain enzymes that work best when there’s some food on the dishes to act on.
4. Deal with hard water
If your glasses come out cloudy or covered in white spots, hard water is the likely cause. Calcium and magnesium in the water leave mineral deposits on dishes and build up inside the dishwasher over time.
Hard water is common in this part of Ontario, especially in communities supplied by wells. For example, Oxford County’s 2025 drinking water report for Woodstock lists a hardness range of 16 to 30 grains per gallon, which is considered very hard. You can find your own water hardness in your municipality’s annual drinking water report.
To reduce spotting:
- Use rinse aid. Keep the rinse aid dispenser full. It helps water sheet off dishes instead of drying into spots.
- Use a detergent made for hard water. Some detergents are formulated to handle minerals better than others.
- Clean the dishwasher monthly. Run an empty hot cycle with a dishwasher cleaner or citric acid to remove mineral scale from the tub, spray arms, and heating element.
- Check for a built-in softener. Some dishwashers, mainly European brands, have a built-in water softener that uses dishwasher salt. Check your manual to see whether yours does and how to set it.
- Consider a whole-home softener. If your water is very hard, a softener protects your dishwasher, water heater, and plumbing.
5. Check the detergent and dispenser
If you find undissolved detergent or a pod still in the cup after a cycle, check that tall dishes aren’t blocking the dispenser door from opening. Make sure the door opens and closes freely, and clear away any caked detergent. If the door latch or spring is broken, the dispenser can be replaced.
Store detergent in a cool, dry place. Powder and pods that absorb moisture clump and dissolve poorly. Use the amount recommended on the package, and use more for very hard water.
6. Make sure the water is hot enough
Detergent works best in hot water. Most dishwashers need incoming water of around 49°C (120°F). Before starting a cycle, run the kitchen tap until the water is hot, so the dishwasher fills with hot water instead of the cold water sitting in the pipes. This matters most when the kitchen is far from the water heater.
If your dishes are coming out cold and wet even with hot water going in, the dishwasher’s heating element or thermostat may have failed.
7. Check that it fills and drains properly
A dishwasher that doesn’t take in enough water can’t clean properly. If you hear it running but little water enters the tub, the water inlet valve or float switch may be faulty.
If dirty water stays in the bottom after a cycle, clean the filter first. Then check that the drain hose isn’t kinked behind the dishwasher. If the dishwasher drains through a garbage disposal that was recently installed, make sure the disposal’s knockout plug was removed. If it still won’t drain, the drain pump may need replacing.
When to call a technician for a dishwasher not cleaning
Call for a repair if you’ve cleaned the filter and spray arms, loaded carefully, used rinse aid, and your dishes are still dirty. Also call if you notice any of these signs:
- The spray arms don’t spin during a cycle.
- The dishwasher hums but doesn’t wash.
- Water doesn’t fill the tub or doesn’t drain.
- Dishes come out cold, or the dishwasher leaks.
Having trouble with other appliances? See our guides to common dryer problems and whether to repair or replace a washing machine.
Frequently asked questions
Why is my dishwasher not cleaning the top rack?
The upper spray arm is probably blocked or not spinning. Clear its holes, make sure nothing in the lower rack is stopping it from turning, and check that tall items aren’t blocking the water feed at the back of the upper rack.
How often should I clean my dishwasher filter?
About once a month for most households. Clean it more often if you run the dishwasher daily or don’t scrape dishes well.
Why are my glasses cloudy after the dishwasher?
Usually because of hard water minerals. Use rinse aid and a hard-water detergent. If the cloudiness doesn’t come off with vinegar, the glass may be etched, which is permanent and often caused by using too much detergent with soft water.
Should I rinse dishes before putting them in the dishwasher?
No. Scrape off food scraps, but skip rinsing. Enzyme-based detergents clean better when there’s some food residue on the dishes.
Is it worth repairing a dishwasher?
Many dishwasher repairs, like a drain pump, inlet valve, or dispenser, are affordable. For major repairs on an older machine, use the same 50% rule we explain in our washing machine repair-or-replace guide.
Which areas does Fixton Appliance Services cover?
Fixton repairs dishwashers, washers, dryers, and other home appliances in London, Woodstock, St. Thomas, Strathroy, Tillsonburg, Ingersoll, Aylmer, and St. Marys, Ontario.
Need dishwasher repair?
If your dishwasher still isn’t cleaning after these checks, Fixton Appliance Services can diagnose the problem and give you a clear quote. We serve homeowners in London, Woodstock, St. Thomas, Strathroy, Tillsonburg, Ingersoll, Aylmer, and St. Marys. Request service online or call us at (548) 800-5995.
