It can be tricky to diagnose a dishwasher that doesn’t drain properly because there are many possible reasons, some of which may not even involve the dishwasher itself. Sometimes, the plumbing may have problems you must fix before considering repairs or replacing the dishwasher.
Before troubleshooting, remember that some dishwashers normally retain a small amount of water at their tub bottom after a complete wash cycle. If you notice a tiny pool of water in your appliance, check the manufacturer’s guide (or contact them) to confirm if it’s normal.
Dishwasher Troubleshooting Relating to the Plumbing
Surprisingly, dishwasher drain problems often originate in the external drain parts, not within the appliance. You may only need to complete some of the following steps. Continue until you identify the culprit behind the dishwasher’s drainage issues. If the fault isn’t found with one of these plumbing-related issues, diagnose problems with the appliance.
Assess the Garbage Disposal
The drain hose in the dishwasher usually connects to the garbage disposal. The buildup of food or other substances inside the disposal can clog it and obstruct the flow of wastewater from the disposal. While running the disposal, run plenty of water thoroughly to clear it. This may resolve your dishwasher’s drainage issues.
Clean the Air Gap
The air gap is the small (typically chrome) cylinder on the kitchen sink’s back edge. It prevents the formation of air vacuums which, in turn, prevents the siphoning of drain water back into the dishwasher. If the air gap brings out water as you run the dishwasher (at times, this water ends up all over the counter), the clog is between the garbage disposal and the air gap.
To clear it, you’ll need to clean the air gap by first removing the air gap cap. Then, disconnect the hose from the nipple at the bottom of the air gap to the sink drain or disposal, and ensure there isn’t any blockage.
Assess the High-Loop
If there’s no air gap on your dishwasher, its drain hose may be attached in a loop to the countertop’s bottom near the sink. Though this doesn’t comply with the code in most areas, it works in the same way as the air gap — preventing the siphoning of drain water back into the dishwasher.
If this drain hose comes loose, meaning it no longer loops at a higher level than the dishwasher, it may stop water from correctly draining out of the appliance. To fix this issue, return the hose to its right high-loop position, or install an air gap.
Tip: If you recently installed a garbage disposal, ensure to knock out the plug inside the nipple of the drain hose. In new disposals, a little plastic disc usually covers the drain opening, and you must remove it with a hammer and screwdriver; otherwise, the dishwasher won’t drain into the disposal. This disc falls into the grinding chamber of the disposal, where you can find and remove it.
Dishwasher Troubleshooting Relating to the Appliance
If there are no noticeable plumbing-related causes, drainage issues may originate from several components on the dishwasher.
Clean the Filter
Dishwashers come with different filter designs. While some have a simple screen or removable filters under the screen, others require the removal of the bottom spray arm for thorough cleaning. Confirm your cleaning requirements from the owner’s manual.
Assess the Drain Screen
The drain screen is located at the dishwasher tub base and should be free from any blockages, including plastic lids, labels, glass, and tiny plastic bits that can cover the drain. You’ll need to look closely to find and clear them.
Assess the Drain Hose of the Dishwasher
This drain hose is normally a corrugated plastic tube running from the air gap, sink drain, or garbage disposal to the bottom of the dishwasher.
Pull out the dishwasher plug or switch off the circuit breaker to disconnect the power to the dishwasher. Take out the toe-kick panel and loosen the hose clamp that secures the drain hose to the pump (have a sponge nearby to soak up any water spill).
Clean the hose end and blow into it. If the hose is connected and you can’t blow air through it, remove the clamp on the other hose end and clean it out in a sink. If you still can’t unblock the hose, or if it’s cracked and old, replace it.
Replace the Dishwasher
It can be expensive to engage an appliance repair specialist, and if your dishwasher is over 9 years old and these fixes don’t solve the drainage issue, you may need to replace the dishwasher.
This project is quite easy, and most homeowners do it themselves, though some appliance stores offer a free installation of the new dishwasher as part of your purchase and may even dispose of the old appliance.
When Should You Call a Professional?
If your dishwasher is still relatively new and isn’t in any way due for replacement, you’ll want to determine how to fix it. If the above fixes don’t resolve the drainage problem, several dishwasher parts could be responsible.
Most replacement parts are readily available online, and you can use your appliance’s model number to find the right ones. The likely culprits are:
- Check valve
- Drain pump and motor
- Piston and nut assembly (on the drain pump)
- Pump solenoid
- Door switch
- Belt (on belt-driven pumps)
- Electronic control
You’ll require some knowledge of electrical circuits and a multimeter to check many of these replacement parts. Unless you are familiar with this diagnosis, leave it to a professional.
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