Dishwashers stopped being a luxury ages ago and are now found in nearly every home. But like any piece of technology, this handy appliance can sometimes let you down. One common issue is when the dishwasher doesn’t drain properly. In some cases, it’s something you can sort out yourself. But when the machine isn’t draining, it can be tricky to get to the bottom of it – there are lots of possible reasons, and some aren’t even to do with the dishwasher itself. Sometimes the problem lies elsewhere, and those external issues need fixing before you consider repairing or replacing the appliance. In this article, we’ll go through the most common causes and suggest what you can do to put things right.

Blocked filter

Before putting plates or cutlery into the dishwasher, you should always scrape off any leftover food. Most user manuals actually recommend giving items a quick rinse before loading them in. But no matter how careful you are, tiny food particles will still end up on your dishes.

As soon as the programme starts, those bits of food are washed away with water and detergent. They all end up at the bottom of the dishwasher’s cleaning chamber – and that’s where the drain filter sits. This filter is often called the “waste” or “debris” filter, because it’s designed to catch all the food particles. That’s exactly why it gets clogged up fairly quickly and needs to be cleaned regularly and properly to keep the dishwasher draining as it should.

It’s really important to keep the drain filter spotless, which is why some dishwasher manufacturers include self-cleaning filters. After all, most people don’t think to clean the filter regularly. If your dishwasher has a standard (manual) filter, it’s recommended to clean it after every wash cycle – or at the very least, once every couple of months. A clogged filter can stop your machine from working properly.

Important! Before cleaning the filter, switch the dishwasher off at the mains. If there’s any water sitting in the bottom of the machine, mop it up first. Only then should you remove the filter and give it a clean.

The filter is easy to take out, and all parts can be rinsed thoroughly under running water. You can also use cleaning products if the filter is particularly dirty – dishwashing liquid, laundry soap, bicarbonate of soda, table salt, vinegar or citric acid solution all work well. You can use a soft brush for scrubbing, but do so carefully to avoid damaging any parts.

Problem with the drain hose

If your dishwasher can’t drain properly, it won’t be able to collect any more water. Start by checking the position of the drain hose connected to the machine. It should be attached to the waste pipe at a height of at least 50 cm and no more than 100 cm above the floor. The drain hose can be connected either to a separate waste outlet or to the sink’s waste pipe. If the dishwasher isn’t draining and either of these outlets is blocked, the water won’t be able to leave the machine. To check whether the pipes are blocked, try pouring a bit of water into them. While it drains, inspect the hose and reconnect it properly if needed. You can try using a plunger or a pipe-cleaning product to clear any blockages. If the issue keeps coming back, it’s best to get in touch with a qualified plumber.

Blocked dishwasher drain

If your dishwasher isn’t draining fully, it’s worth knowing that bits of leftover food and small items left on plates can build up inside the drain hose during use. Another common place for a blockage is the waste pipe itself. To work out where the blockage is, get a container ready to catch the water, then disconnect the hose and direct it into the container. Switch the dishwasher to drain mode. If the water flows out at good pressure, the issue is likely with the waste pipe. You can try clearing it using a drain cleaning product. If that doesn’t work, you may need to use a drain rod or flexible cable to break through the blockage. If the water only trickles out of the hose, then the hose itself is probably blocked. In that case, remove it and rinse it through with a strong jet of water.

Solution: Call a plumber, or try unblocking it yourself using a drain rod, plunger or a chemical drain cleaner. A homemade solution of vinegar and baking soda or soda crystals can also do the trick in some cases.

Drain pump failure

If your dishwasher isn’t draining and there are no blockages in the waste path, the issue might be a weak or faulty drain pump. In most cases, when the pump fails completely, the machine will stop altogether and won’t drain at all. However, if the pump is still partially working, it may keep trying to pump the water out – sometimes endlessly, without success. To get a proper diagnosis, it’s best to contact a qualified appliance repair specialist. They’ll be able to tell you whether the drain pump needs replacing or if the problem lies elsewhere.

Faulty drain pump motor

A problem with the circulation pump – which supplies water to the spray arms – can also stop your dishwasher from draining properly. If the pump has failed, it usually needs to be replaced with a new one. To do this, you’ll need to access the bottom of the appliance, disconnect all pipes and fixings from the unit, and then fit the new pump in place.

You can often recognise a faulty circulation pump by the sound it makes – or rather, doesn’t make. If the dishwasher fills with water but you don’t hear the usual humming noise, the pump might not be working. As you can see, replacing the pump isn’t especially difficult. There’s also the drain pump, which is responsible for removing dirty water. If this part fails, the dishwasher won’t drain at all – and it’s usually clear that water is stuck inside. In most cases, a broken drain pump can’t be repaired and will need to be replaced.

Problem with the water quality sensor

The water quality sensor – sometimes called the aqua sensor – helps the dishwasher work out how clean the water is by checking how much light passes through it. This helps the machine decide whether the dishes are properly washed or if it needs to keep going. If the sensor gets dirty or blocked, the dishwasher might carry on running but won’t finish the cycle properly – and it could end up using more water than usual. If there’s a build-up of grease on the sensor, you can remove it and clean it with a degreaser. Sometimes, a hard white crust (often from salt) can form on the surface. In that case, gently scrape it off using a small screwdriver. If cleaning doesn’t fix the issue, you may need to replace the sensor yourself or call out a technician.

Summary

• Make sure your dishwasher is installed correctly and in line with the manufacturer’s guidelines – incorrect installation can stop it from draining properly.
• Clean the filters at least once every two months.
• Don’t overload the dishwasher with too many dishes.
• Consider installing surge protection to guard against voltage drops.
• Always scrape off leftover food before loading your dishes.
• Use high-quality detergents for the best results.

And don’t forget – not every problem can be fixed at home. Dishwashers are getting more advanced every year, with increasingly complex features and components. Without the right tools or technical knowledge, it’s best not to attempt repairs yourself. When in doubt, call in a professional.