Machine descaler


A blocked dishwasher will present different symptoms depending on which area is blocked. If there is a problem with the draining system or plumbing, then you will most likely find that water starts to accumulate at the bottom of the machine. You may also notice a bad smell, which is caused by a build-up of bacteria, minerals and food in the water. Whereas, if the spray arms are blocked then you may find that your dishes are coming out of the dishwasher less clean than usual, but you might not have excess water at the bottom of your machine.

If you have noticed all of these symptoms, then it’s likely that more than one part requires cleaning. Once you’ve identified that your dishwasher is blocked, you can begin the process of cleaning it out.

Why is My Dishwasher Blocked?

Over time your dishwasher will accumulate pieces of food, grease, hair, and even broken glass or ceramics. This can all build up in various parts of your dishwasher, causing it to perform poorly.

Luckily, the most common dishwasher blockages are relatively straightforward to clear and don’t require you to have expert knowledge. In this guide, we will walk you through the most common causes of a blocked dishwasher and how to clear a blocked dishwasher.

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Step by Step – How to Fix a Blocked Dishwasher

When it comes to troubleshooting your dishwasher and finding out where the blockage is, it is best to start from the simplest part to clean, and build up to the most awkward or difficult parts to clean. The following steps will guide you through the process, and if you are lucky, you will fix your problem within the first few steps. Otherwise, we have you covered with what to do next.

1.      Prepare your area & detach the dishwasher from the power source

The first step before investigating your washing machine is to switch it off at the mains and unplug it from the wall. After you’ve done this, grab an old towel or two and have them handy, as during the next steps you are likely to have to mop up some water while you are fixing the blockage.

2.      Prepare your dishwasher.

Next, you will want to get your dishwasher ready. Remove the baskets from the machine, as you will need space to access the parts. If you have a lot of cloudy standing water, remove as much of the water from the machine as possible, so you will have a clear view. You can remove the water using a sponge to absorb the water, ring it into a container, and repeat until the standing water is mostly removed from the bottom of the machine. Always be careful as there could be broken glass at the bottom of a dishwasher.

3.      Unblock the filter.

Your washing machines filter is the most common area for a blockage to occur since it is the first line of defence protecting the pump from debris. Luckily, it is also the easiest part to clear a blockage from.

The filter is typically located at the base of the machine, underneath the spray arm. You will have to remove the bottom spray arm, which should either just pull off, or it may need a bolt undone. The filter should have a cover and usually comes in 3 parts, which will all either pull or twist out.

In order to clean it out, take the pieces apart, and scrape off as much of the debris as possible into a bin. Putting it all down the sink will likely just result in a blocked sink. Once you have got most of the gunk off, you can use an old toothbrush to clean the mesh with hot soapy water and get into any crevices. Rinse it off once clean and prepare for putting back into the machine.

In order to avoid future blockages, you should clean the dishwasher filter frequently. For example, if you use your dishwasher every day, then you should clean the filter once every week or two to prevent too much build-up.

4.      Unblock the impeller or propeller

Underneath the filter, there will be a cover that protects the propeller (also known as an impeller). Although the cover is designed to protect the propeller from debris, sometimes things can get behind the cover and become trapped in the propeller. If this happens, your dishwasher won’t drain correctly.

To check the propeller and clean it out, you will first need to remove the cover. The cover usually will pop out, but can sometimes be a tight fit, so tweezers or a blunt butter knife may be useful to help you remove it. Once it’s off, you should check if the propeller turns freely and that nothing is caught inside it, preventing it from turning.

If there is something trapped inside, you can use a toothbrush, toothpick or tweezers to remove any debris.

Remember to replace the propeller cover before putting the filter back in.

You can check the dishwasher’s manual to see which other parts of the sump are accessible, as this will show you other areas that you can check for blockages.

5.      Unblock the spray arms.

Blocked spray arms won’t contribute to draining problems, but if you’ve noticed that your dishes are coming out of the dishwasher less clean than they usually are, then you might have blocked spray arms.

If you’ve already followed the steps above, you will only now have to remove the top spray arm. It should either pull or twist off, but sometimes they have a bolt that needs undone.

Once you’ve got both of the arms off, you will want to run them under a tap and see if water drains through all of the little holes. If any holes don’t let the water pass freely through them, then they are likely blocked.

Soak the spray arms in hot soapy water, or run them under a hot tap. You can use a toothbrush or toothpick to clean out stubborn debris.

Once water can run freely through all of the holes on the spray arms, then you can rinse them off ready to go back in.

6.      Check if the hose is bent or blocked.

If your dishwasher still won’t drain, then the next step will be to look for a bend or blockage in the hose. This step should be relatively straightforward as long as you don’t have an integrated washing machine. If you do, you will probably have to hire a professional to fix the issue since you won’t be able to access the back of your machine.

First of all, make sure that the wastewater pipe isn’t kinked, or crushed, as this will restrict flow and prevent successful draining. Your dishwasher may not have been secured, or it may have broken away from its restraints. This can allow it to move around, and it may have moved backwards, squashing the drain hose. If you can, gently pull the dishwasher away from the wall. Be careful not to pull it too far out, as the water supply and drainage hose are both attached at the back. Locate the drainage pipe at the back of the machine. It is usually a white or clear accordion pipe and will be larger than the water supply pipe.  If everything looks ok, then the next step is to treat it as a blocked dishwasher drain pipe.

In most cases, your dishwasher drain pipe will connect to your sinks drain. If this is the case, you may have a blockage in the U-bend underneath the sink. If this is the case though, you will likely also have problems with your sink draining, and it might smell. If this is the case, then you should pour soapy boiling water down your sink. Repeat this several times in order to aid the break-down of grease which might be holding together debris. You can also use a plunger to help dislodge any obstructions.

If this hasn’t helped, then you may need to remove the washing machines drain pipe. Removing the pipe may prove to be quite an undertaking depending on your dishwasher make and model. Before removing the pipe, you can try squeezing it all the way along to try to break up any blockages. If this doesn’t help, the next step is to remove the pipe and give it a clean. In some cases, your washing machine will have a kick panel on the front which will give you access to where the pipe is attached to the machine. However, some machines will require you to remove a plate which is screwed onto the underside in order to gain access.

If you are able to access the area where the pipe attaches, then you can try to remove it. Put a tray or towel underneath your working area to catch drips and leaks. Some of the washing machine manufacturers connectors are not designed to be reused, so you will have to look at your manual to find out if you will also need to purchase a new connector. Once you have successfully removed the pipe, you can remove it at the other end too, this is usually underneath your sink. You can clean the pipe out either by pouring soapy boiling hot water down it, taking it outside and using a hose on its highest pressure setting or by using a long flexible brush.

After you have cleaned the blockages out, you can reattach the pipe at both ends and close up the machine.

Run a short cycle to ensure that there are no leaks, and check if the water drains away.

7.      Call a professional

If you have followed the advice above and your dishwasher is still not draining, then you may have a fault with your machine, such as the pump. Alternatively, you may have an issue with your plumbing. In any case, your best bet from here on is to hire a professional to assess what the problem is. They will be able to diagnose the problem and offer a solution.



If you’ve followed these steps, not only will you have likely fixed your dishwasher all by yourself, you now also have a sparkling clean machine! In order to avoid future blockages, you should try to keep on top of cleaning your filter regularly, as this will help prevent build-up further down the waste pipe. You should aim to clean it once every week or two if you’re using your dishwasher every day. Another important step is to ensure you clean off as much leftover food from the plate as possible before placing it into the dishwasher, this will save you cleaning as much gunk out of the filter.

Make sure that when you are cleaning blockages you are only using chemicals that are safe to use in the dishwasher. For example, drain unblockers should never be used in your dishwasher, or to clean any parts of your dishwasher, even if you are struggling to clean out a blockage. These products can leave behind residues that are harmful if ingested.

Skills Training Group is an award-winning provider of gas apprenticeship, plumbing, electrical & first aid courses. For further information on our range courses, contact a member of our team on 0141 889 4516.

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