How to unblock dishwasher: UK guide to quick fixes

That sinking feeling when you open the dishwasher to find a pool of murky, greasy water is never a welcome sight. It’s a sure sign of a blockage, but don’t panic just yet. More often than not, the culprit is something simple: trapped food debris in the filter, a kinked drain hose, or a clog where the hose connects to your sink's plumbing.

Learning how to unblock your dishwasher usually starts with these straightforward checks, and you can often get things flowing again without calling in a pro.

Why Your Dishwasher Is Blocked

Before you start pulling your appliance apart, it’s worth playing detective for a moment to pinpoint the likely cause of that standing water. Different symptoms can give you some surprisingly useful clues about where the problem is hiding.

Is your dishwasher making strange gurgling sounds as it tries to drain? That often points towards a partial blockage in the drain hose or at the sink connection. On the other hand, if a foul smell is the first thing that hits you, it’s a good bet that old food and grease are decaying in the filter or the sump area just beneath it.

With dishwashers becoming a staple in UK kitchens, these minor blockages are a common household headache. In fact, with the UK dishwasher market expected to grow, it highlights just how much we rely on them.

To help you get started, here’s a quick way to diagnose the problem like a pro.

Quick Diagnosis: Common Dishwasher Blockage Signs

This table should give you a solid starting point. This guide will walk you through the fixes for these common issues, starting with the simplest ones first.

Clearing the Dishwasher Filter and Sump Area

Nine times out of ten, the reason your dishwasher won't drain is a clogged filter. This little component is your machine's first line of defence against all the food bits left on your plates. Thankfully, giving it a clean is usually a quick fix you can sort in less than 10 minutes.

You'll find the filter assembly right at the bottom of the dishwasher, usually hiding under the lower spray arm. It’s typically made of a coarse outer filter and a fine inner mesh, and most just twist and lift right out.

Take both parts over to the sink and give them a good scrub with warm, soapy water to get rid of any grease and trapped food particles. For a really spotless finish, it’s worth checking out our full guide on how to deep clean a dishwasher.

With the filter out, take a moment to peer into the sump—that's the little well it sits in. Have a wipe around and clear out any gunk you find in there. More often than not, this simple clean-out is all it takes to get your dishwasher draining like new again.

Checking and Clearing the Drain Hose

So, you've cleaned the filter and sump, but your dishwasher is still stubbornly holding onto water. The next likely culprit is the drain hose itself.

Before you start unscrewing anything, it’s worth taking a quick peek behind the appliance. Sometimes, the hose gets pushed against the wall, creating a sharp kink that stops water in its tracks. A simple adjustment to straighten it out could be the quick fix you need.

If the hose looks straight, the blockage is probably lurking inside. First, get a bucket and some old towels ready. Place them directly under where the hose connects to either the dishwasher or your sink's plumbing.

Once you’ve carefully detached the hose, you can try to flush out the gunk. Holding it under a tap in your sink and running water through it often dislodges most food-based blockages. For tougher, greasy build-ups, a classic mix of bicarbonate of soda and vinegar can work wonders to break it down.

Remember, the dishwasher drain hose usually connects to your sink's plumbing. This means a blockage in your sink drain can easily cause water to back up into the dishwasher. If you suspect this might be the case, our guide on how to unclog a kitchen sink has some extra tips that could solve the problem for good.

Have a Look at the Spray Arms and Sink Connections

Sometimes, the blockage isn't deep down in the pipes. If your dishes are coming out grimy and there's still water sloshing around at the bottom, the problem could be as simple as clogged spray arms.

It’s an easy one to check. Just carefully take the spray arms out – they usually clip or twist off. Grab a toothpick or a small bit of wire and gently poke out any bits of food or limescale you see clogging the little holes. This alone can make a huge difference to your dishwasher's performance.

Check the Sink and Waste Disposal

Another very common culprit, especially if you've had a new dishwasher or sink installed, is the connection to the waste disposal unit under your sink. There's a small plastic piece inside the connection spout called a knockout plug. It has to be removed for the dishwasher to drain properly. It’s surprising how often this gets missed during installation!

It's also worth thinking about what's going down your drain. In the UK, grease and limescale are the top offenders for causing blockages, which is why you see so many specialised dishwasher cleaners on the supermarket shelves. Having a basic grasp of things like understanding floor trap drains can sometimes shed light on recurring drainage issues.

When Your DIY Fix Isn't Enough

So, you've cleaned the filter, checked the hose, and given all the connections a once-over, but that stubborn puddle of murky water is still sitting at the bottom of your dishwasher. It’s frustrating, and it’s usually the point where the problem is a bit more complicated than a simple blockage you can sort out yourself.

Certain issues, like a faulty drain pump or an electrical fault, really do need an expert’s touch. A key giveaway is a persistent humming noise coming from the pump area, even when it’s not draining. This is a clear sign to stop troubleshooting. For a deeper dive into drainage problems, this comprehensive guide on clearing blocked drains offers some great insights.

At this stage, calling in a professional is the safest and most reliable way to get things fixed properly. If you're not sure where to start, have a look at our tips on how to find a good plumber.

Got Questions? We've Got Answers

Here are some of the things our engineers get asked all the time – and the expert answers you need.

How often should I be cleaning my dishwasher filter?

To keep blockages at bay, you should aim to clean your dishwasher filter at least once a month. If you use your dishwasher daily or you’re not the best at scraping plates before loading, then a quick rinse once a week is an even better habit to get into.

Why does my dishwasher smell so bad?

That unpleasant pong is almost always down to old food particles and grease that have got trapped and are now rotting away. The main culprits are the filter, the sump area at the bottom, or even the drain hose itself. A good clean-out usually sorts it. For a fresher machine, try running an empty, hot wash cycle with a proper dishwasher cleaner.

Can I just pour a chemical drain unblocker in there?

Please, absolutely not. Those harsh chemical unblockers are made for tough sink pipes, not the delicate internal parts of your dishwasher. Using them can easily eat away at the plastic components, rubber seals, and hoses. You could end up with a repair bill far bigger than the original blockage. Stick with manual cleaning methods or gentle solutions like bicarbonate of soda and vinegar.

If you've given all the DIY fixes a go and your dishwasher still isn't playing ball, it’s time to call in the experts. The issue could be something more serious, like a failing pump or a blockage deep in the plumbing that needs an expert eye.

For a fast, reliable, and guaranteed fix, book one of our qualified Go Assist engineers today. Let’s get your dishwasher back to doing what it does best.