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That pool of water sitting at the bottom of your dishwasher after a cycle is never a good sign. But before you assume the dishwasher itself has packed it in, it is worth checking the plumbing around it.
In many cases, the culprit is a surprisingly simple fix. A blocked filter can stop water from draining properly and is often something you can sort out in a few minutes. But if your kitchen sink is also draining slowly, water is backing up, or other drains around the home are playing up, the problem may be further down the line!
We break down the common reasons your dishwasher won't drain, including the plumbing problems that can sit behind the issue. We will cover the safe checks you can try yourself, what to avoid, and the warning signs that it is time to call in a plumber.
At the end of a wash cycle, the dishwasher uses a pump to push wastewater out of the tub and through a corrugated drain hose. The hose typically runs beneath the benchtop or through the cabinetry before connecting to the kitchen sink’s waste plumbing.
Depending on how your kitchen is set up, the hose may connect directly to a dishwasher spigot on the sink trap or another suitable waste connection. Some Australian kitchens also have an air gap, usually fitted near the sink or benchtop. The drain hose runs through this fitting before connecting to the waste pipe, helping prevent dirty water from siphoning back into the dishwasher.
So while the dishwasher and sink are separate appliances, they ultimately rely on the same drainage system to get rid of wastewater.
| Why Does the Drain Hose Need to Be Positioned Correctly?The position of the dishwasher drain hose matters, too. It should generally rise into a high loop underneath the benchtop before dropping down to the waste connection.This high loop helps prevent wastewater from the sink flowing backwards through the hose and into the dishwasher. If the hose has slipped down, been pushed out of position or was installed incorrectly, you may notice dirty or smelly water returning to the dishwasher after a cycle. |
Once you have ruled out an obvious internal fault, here’s what to consider:
The filter is one of the first things to check, and one of the most common causes of a dishwasher that will not drain. Most modern dishwashers have a removable filter at the bottom of the tub that catches food scraps and other debris before they enter the drainage system.
Over time, grease, food particles and other residue can build up and restrict water flow.
If the dishwasher starts draining normally after cleaning the filter, you may have found the problem. If it is still holding water, it is time to look further along the drain path.
The drain hose carries wastewater from the dishwasher to your kitchen's waste plumbing. If that hose becomes blocked, crushed or sharply kinked, water cannot get out of the machine properly, even if the dishwasher filter is clean.
A common cause is the dishwasher being pushed back too far after installation, cleaning or a repair, trapping the hose against the cabinetry or wall.
Avoid pulling the dishwasher out aggressively or disconnecting plumbing if you are not confident doing so. A water leak behind an integrated appliance can quickly become a much bigger problem.
The connection underneath your sink is another potential trouble spot. Dishwasher hoses commonly connect to a dedicated spigot on the sink waste or trap, and food debris and grease can build up around this connection.
Some kitchens also have an air gap; a small fitting mounted near the sink or benchtop. If it becomes blocked, you may notice water bubbling, dribbling or spurting from the fitting when the dishwasher tries to drain.
This does not necessarily mean the dishwasher pump has failed. The pump may be working but the water simply cannot get through the blocked connection.
Your dishwasher and kitchen sink share the same waste system, so a problem with the sink can quickly become a problem for the dishwasher too.
Grease, food scraps, coffee grounds and soap residue can gradually build up inside kitchen waste pipes. If the sink is already draining slowly, water is pooling around the plughole, or there is an unpleasant smell coming from the drain, those are useful clues that the blockage may be in the shared plumbing.
In this situation, clearing the dishwasher filter alone is unlikely to solve the problem. The underlying restriction needs to be addressed in the kitchen waste system.
💡 Read more on the causes of blocked kitchen sink drain.
Sometimes the blockage is further down the line, beyond what you can see or safely reach yourself. When this happens, cleaning the dishwasher filter, checking the hose and clearing the visible waste connection might not make much difference.
A plumber can assess the drainage system and, where appropriate, use equipment such as a CCTV drain camera to identify what is happening inside the pipe without relying on guesswork.
💡 Need help with a blocked dishwasher or kitchen drain? We’ve got it covered
Not every drainage problem is caused by a blockage. Incorrect installation can create drainage and backflow issues from the very first wash.
If the drain hose has not been installed with the appropriate high loop or air-gap arrangement, or has been routed incorrectly, wastewater can flow back towards the dishwasher. This is particularly worth considering if the problem started immediately after a new dishwasher was installed, a kitchen was renovated or plumbing work was carried out.
If the dishwasher has recently been installed or moved, let your plumber know. It can be an important clue when diagnosing the problem.
Not every dishwasher that refuses to drain needs a plumber. If the plumbing checks out but the problem remains, the appliance itself may be responsible. A loud humming sound during the drain cycle without any water movement can indicate a jammed or failed drain pump. Complete silence when the machine should be draining may point towards an electrical or control fault, while a faulty door latch can also interrupt the dishwasher's cycle.
Some machines will display an error code when a drainage or control fault occurs, so it is worth checking the manufacturer's instructions for your particular model.
A good number of dishwasher drainage problems are solved at this stage, without needing to call anyone at all. Work through these in order.
1. Switch It Off First: Turn the dishwasher off at the wall before you do anything else. You will likely be working around standing water, and there is no reason to have it powered while you do.
2. Clean the Filter: Remove the bottom rack and find the filter assembly, usually a round or cylindrical piece that twists out at the base of the tub. Rinse it under warm running water and scrub it with an old toothbrush until no grease or debris remains, then check the seat it sits in before clicking it back into place. This single step resolves the majority of dishwasher drainage complaints.
3. Check for Visible Debris: Look for anything obviously caught around the base of the tub, such as a piece of broken glass, a bottle cap, or food scraps. Remove anything you can see safely by hand. Do not force anything, and do not push objects further into the drain to try to clear them.
4. Check Under the Sink: Open the cabinet under the sink and look at the drain hose. You are checking for an obvious kink, a loose connection, or any sign of a leak where the hose meets the sink trap or the air gap fitting. If your kitchen has an air gap, unscrew the chrome cap on the benchtop and check the small chambers inside for built-up grease.
5. Run a Short Test Cycle: With the filter cleaned and no visible blockage, run a short rinse cycle and watch how it drains. Slow drainage, gurgling, or water backing up into the sink all tell you something. If it drains cleanly, you are done. If not, move on to checking whether the sink itself is draining properly, which is the single biggest clue in this whole process.
❌ Do not pour chemical drain cleaner into a dishwasher. These products are designed for open sink drains, not a sealed appliance with rubber seals, a pump, and electrical components, and they can cause real damage.
❌ Do not force the hose, the fittings, or the pump.
❌ Do not dismantle plumbing connections you are not familiar with. A wrongly reassembled trap under the sink is a much bigger and messier problem than the one you started with.
✅ Scrape plates before loading rather than relying on the dishwasher to deal with food scraps
✅ Clean the filter at least once a month
✅ Avoid pouring cooking oil or grease down the kitchen sink, since it is one of the most common causes of the shared drain blocking in the first place.
✅ If your home has older pipework or you have had recurring drainage issues before, a periodic drain inspection can catch a developing blockage before it turns into an emergency.
Some dishwasher drainage problems are easy enough to troubleshoot yourself. But if you have worked through the obvious checks and the water still is not going anywhere, it is usually better to call a plumber than keep guessing.
A dishwasher that won't drain is frustrating, but it does not always mean the appliance itself has failed.
The easiest place to start is with the simple checks: clean the filter, inspect the accessible parts of the drain hose and check whether your kitchen sink is draining normally. If the dishwasher and sink are both slow, water is backing up, you notice gurgling or the problem keeps returning, there is a good chance you are dealing with a plumbing issue rather than an appliance fault.
That is where it pays to get the problem properly diagnosed rather than repeatedly trying quick fixes.
Plumberoo can help identify and clear blocked kitchen drains, inspect dishwasher waste connections and get your drainage system flowing properly again. Whether it is a stubborn blockage, recurring drainage issue or something deeper in the pipework, our experienced plumbers can find the cause and recommend the right fix. Get in touch today.