How to fix a dishwasher that will not drain
Opening the dishwasher to a pool of dirty water is grim, but it is rarely a serious fault. Nine times out of ten a blocked filter, a kinked hose, or a clogged sink waste is to blame, and all three are things you can put right yourself in a few minutes. This guide walks you through the fixes in the order most likely to work, safely, and shows you the point at which it is worth calling an engineer.
Before you start: two quick things
These two steps make the whole job cleaner and safer, so do them before you touch anything else.
Two minute prep
- Switch off the power. Turn the dishwasher off at the socket or isolator switch. You are about to work near standing water, so cut the electricity first.
- Bail out the water. The tub is usually full. Scoop out as much as you can with a jug or cup, then soak up the rest with towels or a wet vacuum. Skip this and the water will flood your floor the moment you lift the filter.
Guided fix walkthrough
Work through the checks in order. Each one is more likely to be the culprit than the next, so start at the top and only move on if the water still will not clear.
Interactive Drain fix walkthrough
Check 1 of 5
The usual suspects, ranked
If you would rather understand what tends to go wrong before you dive in, here are the causes from most to least common.
Food debris collects in the filter at the base of the tub. A clogged filter is the single most frequent reason a dishwasher stops draining.
The hose behind the machine gets pinched when it is pushed back into place, or silts up over time.
The dishwasher drains into your sink waste, so a clogged trap stops it too. On a new install, the knockout plug in the waste spigot is often left in by mistake.
A shard of glass, a fruit stone, or a bit of plastic can stop the drain pump impeller from turning.
A failed drain pump or a stuck one way valve stops water leaving, and both are engineer jobs.
Excess suds can interfere with draining. Use the correct dose and a proper dishwasher detergent, never washing up liquid.
Stop it happening again
Most drainage problems are avoidable. A few small habits keep the water moving.
- Scrape plates before loading. You do not need to rinse, but remove bones, seeds, and stickers.
- Rinse the filter every week or two under the tap.
- Run a hot maintenance cycle with a dishwasher cleaner once a month.
- Keep the drain hose free of kinks whenever you move the machine.
- On a new install, check the waste knockout plug is out and the hose has a high loop.
- Keep salt and rinse aid topped up on models that use them.
Work safely
Always switch the dishwasher off at the socket or isolator before reaching inside or behind it. Wear gloves when clearing the filter or pump, as broken glass often collects there. If you find water leaking onto the floor, stop, switch off at the mains, and have it checked rather than running another cycle.
When to call an engineer
You have done everything reasonable at home if the filter, hose, sink waste, and pump area are all clear and the machine still will not drain. At that point it is likely the drain pump, the check valve, or the control board, and those need a professional.
Call an engineer if the pump hums but no water moves, if a drain fault code keeps returning after you have cleared the blockages, or if water is leaking underneath the machine. The reassuring part is that a single component is far cheaper than a new dishwasher. Every CATA appliance comes with a 5 year parts and 2 year labour warranty when you register within 30 days of purchase, backed by a nationwide network of approved engineers.
Frequently asked questions
Standing water usually means the dishwasher cannot pump waste away, most often because the filter, drain hose, or sink waste is blocked. A small amount of clean water in the sump is normal between cycles, but dirty standing water points to a drainage blockage.
Yes, in most cases. Cleaning the filter, straightening the drain hose, and clearing the sink waste are all safe to do yourself once the power is switched off. If the pump has failed or a fault code persists, that is a job for an engineer.
A very common cause is the knockout plug left in the sink waste or disposal spigot, which blocks the drain hose connection. Check this plug has been removed, and make sure the drain hose has a high loop so water cannot siphon back.
Yes. The tub is usually full, so scoop or soak up as much water as you can with a jug and towels first. If you remove the filter with the tub full, the water will run out onto the floor.
This is often the drain hose sitting too low, letting waste water siphon back into the machine. Fitting a high loop in the hose, or checking the anti siphon setup, usually solves it. A faulty check valve can also cause it.
A humming sound with no draining often means the drain pump is trying to run but is jammed by a piece of food, glass, or plastic. If clearing any visible debris does not help, the pump may have failed and needs an engineer.
Key points
- Switch off the power and bail out the standing water before you start.
- Work in order: filter first, then the sump, drain hose, sink waste, and finally the pump.
- A blocked filter is by far the most common cause, and the quickest to fix.
- After a new install, check the waste knockout plug is removed and the hose has a high loop.
- If it still will not drain with everything clear, the pump or valve has likely failed and needs an engineer.
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