Why is my dishwasher not draining?

Water sitting in the bottom at the end of a cycle means the drain path is blocked somewhere between the sump and the drain under the sink, or the pump has failed. The path is short and every part of it except the pump is designed to be checked by the owner, so work along it in order rather than guessing.

Safety

What you'll need

• A jug and a sponge or old towels
• Rubber gloves
• A bowl or washing-up bowl for the drained water
• A screwdriver for the hose clip (optional)
• A torch (optional)

Step by step

1. Switch it off at the socket.Not just the programme button. You are going to reach into the sump, and on many machines there is a chopper blade under the filter that is driven by the wash motor.
2. Bail out the standing water.A jug down to the last inch, then a sponge or towels. You cannot assess anything through a bowl of grey water, and you will spill it on the floor when you tip the machine forward later.
3. Remove and clean the filter assembly.Bottom centre, usually a coarse cylinder that twists a quarter turn, plus a flat fine mesh under it. Rinse both under a hot tap and brush them. A filter caked with grease and starch is the most common single cause.
4. Check the sump underneath the filter with a torch.Look for a fruit sticker, a plastic seal from a milk bottle, a bone fragment or broken glass sitting over the drain outlet. Lift it out with gloved fingers or long tweezers — not with bare hands, because of the glass.
5. Run a drain cycle and listen.Switch the machine back on and select the shortest programme, or the cancel-and-drain function if it has one. A humming or straining noise means the pump is trying and cannot shift water — a blockage further along. Total silence at the point it should drain means the pump is not being driven, which is an engineer's job.
6. Check the waste connection under the sink — this is where a new install fails.Where the dishwasher hose joins the sink trap or waste, there is a moulded spigot with a blanking disc inside it. It must be cut or knocked out before use. A machine that has never drained since it was fitted almost always has an intact blanking disc.
7. Check the sink trap and the waste pipe itself.Undo the trap over a bowl and clear it. A dishwasher drains into the same waste as the sink, so a trap silted up with fat will back the machine up even when the machine is perfect. If the sink also drains slowly, this is your answer.
8. Check the drain hose for a kink and for the high loop.Pull the machine out gently. The hose must rise to at least 600mm above floor level before it drops to the waste, or dirty water siphons back. Look for the hose crushed behind the machine or trapped under a foot.
9. Clear the drain hose itself if everything else is clear.Release the clip, drop the free end into a bucket below the machine and let it gravity drain. If nothing comes out, the hose is blocked — flush it through with hot water at a sink. Grease sets solid in the corrugations of an old hose.
10. Stop and call an engineer if the pump is silent or the machine shows a drain error after all this.A failed drain pump, a blocked pump impeller behind an access cover, or a failed pressure sensor are all internal jobs. Nothing behind the base panel is owner-serviceable on a plumbed-in appliance you cannot safely tip.

Common mistakes

• Pouring drain cleaner into the dishwasher — It is formulated for sink waste, not for a machine full of stainless steel, rubber seals and a plastic pump housing. It will not reach a filter blockage and can damage the seals.
• Tipping the machine forward to empty it — The water goes into the base tray and onto the floor, and on a machine with a float switch the trapped water triggers a lockout that makes the machine look more broken than it was.

If it doesn't work

Questions people ask