Dishwasher not draining? Appliance or drain?

A dishwasher pumps away the dirty water at the end of each rinse cycle via a hose connected under the worktop to the kitchen drain. Usually this goes via a branch on the kitchen sink trap, sometimes via a separate connection in the wall. Water that remains standing therefore means that something is wrong somewhere along that route: in the appliance, in the hose or in the kitchen drain.

Possible causes at a glance

• A full or dirty filter. At the bottom of the dishwasher there is a filter or mesh that catches food residue. If it becomes blocked, the water cannot reach the pump. This is by far the most common cause and you can solve it yourself.
• A kinked or silted-up waste hose. If the dishwasher has recently been moved or something has been placed in the cupboard under the kitchen sink, the hose may be kinked or pinched. Dirt can also accumulate in the hose itself.
• A blocked branch or trap. The point where the hose connects to the trap or wall connection is narrow. Grease and food residue from the kitchen sink and the dishwasher can form a blockage there together.
• A blocked kitchen drain. If the kitchen sink itself is also draining slowly, the dishwasher cannot discharge its water. The dishwasher is not broken; the drain is the problem.
• A defective drain pump or appliance fault. If you no longer hear the pump running, it makes a humming or rattling sound without water draining, or the appliance shows an error code, the pump may be broken or blocked by an object.

Appliance or drain? How to tell the difference

A simple test will get you a long way. Let the kitchen sink fill up with a good amount of water and pull the plug.

• Does the kitchen sink drain slowly or gurgle? Then it's probably the kitchen drain or the trap. That's a job for a plumber, or something you can try yourself first with the steps in kitchen sink blocked.
• Does the kitchen sink drain freely? Then the problem is more likely in the dishwasher: the filter, the hose, the connection or the pump.
• Does water come up in the kitchen sink while the dishwasher is pumping? That's a clear sign that the drain after the trap is narrowed. The dishwasher is doing its job, but the water can't get any further.

Step-by-step plan: what you can check yourself

1. Switch off the dishwasher and unplug it. Never work on an appliance that is still live. Also turn off the water supply tap if present.
2. Scoop out the water. Remove the lower rack and scoop the water into a bucket using a cup or sponge. Place a towel in front of the dishwasher.
3. Clean the filter. Remove the filter at the bottom as described in your appliance manual. Rinse it under the tap and clean it with a washing-up brush. Check that there's no shard of glass, bone or label in the opening underneath.
4. Check the drain hose. Carefully pull the dishwasher forward a little or look in the cupboard under the kitchen sink. Remove kinks and check that nothing is pressing on the hose.
5. Check the connection to the trap. Have a bucket ready and unscrew the hose from the branch. If the opening is blocked, clean it. Also clean the kitchen sink trap straight away.
6. Run a short programme. Plug it back in and select a rinse or drain programme. Check whether the water now drains away and whether there is any leakage under the worktop.

Appliance engineer or plumber?

It is good to be honest about this. A plumber deals with the drain: the trap, the branch, the pipe in the wall and everything behind it. If the drain is blocked, you have come to the right place with us. If the problem is in the dishwasher itself, for example a broken drain pump, a fault in the control system or an error code that keeps coming back after cleaning the filter, that is work for an appliance engineer or the manufacturer of the appliance. If the appliance is still under guarantee, first contact the shop or the manufacturer.

If in doubt, do the kitchen sink test above. If the kitchen sink drains well and the filter is clean, then it's almost certainly the appliance.

What you'd better not do

• Do not pour chemical drain cleaner into the dishwasher or the kitchen sink. Caustic agents can damage the rubber seals in the dishwasher and the trap seals. If the agent remains standing, it's also dangerous when disconnecting the hose.
• Do not keep restarting. A dishwasher that repeatedly tries to pump out whilst the pump is blocked can damage the pump further.
• No boiling water down the kitchen sink to clear the drain. The drain under the worktop is usually plastic and boiling water can deform PVC over time.
• Do not unscrew the appliance yourself if you do not know what you are doing. There are electrical components inside.

How to prevent it

• Scrape plates into the bin before they go in the dishwasher; rinsing is usually not necessary.
• Clean the filter regularly, for example every week or two.
• Don't pour grease down the kitchen sink. It solidifies in the trap, exactly where the dishwasher also drains.
• Make sure the drain hose is free and not trapped by items in the cupboard.

Does the washing machine also drain poorly? Then read washing machine drain blocked.

You can read more about unblocking a kitchen drain on the kitchen sink unblocking page. If you want a general overview of what you can do yourself, see unblock yourself or call the plumber.