Why does my washing machine keep filling and emptying itself?

Self-siphoning through the waste hose — the symptom, the high loop that prevents it, and the machine faults that look similar.

Difficulty: beginner
Time: 30 min
Read: 3 min

Short answer

The machine is siphoning water out of the drum through its own waste hose as fast as it fills. Raise the hose so its highest point is above the drum and clip it there. If the hose is already looped high and it still happens, the fault is the machine's pressure switch or drain valve.

A washing machine's waste hose is connected to a drain that is below the drum. Once water starts flowing down it, atmospheric pressure will keep it flowing — that is a siphon, and only a high point in the hose breaks it.

What you'll need

A hose clip or pipe clip
Something to fix the loop to — a bracket or a clip

Connecting a washing machine and a dishwasher to one waste

Step by step

Confirm the symptom.The machine fills, water audibly runs out at the same time, the cycle takes far too long or reports a fill fault. Look at the drain — you should see continuous flow while it is filling.
Look at the hose route.Follow the hose from the back of the machine to the waste. If it runs downhill all the way, there is nothing to break the siphon.
Find the drum level.Roughly the middle of the machine's height. The top of the hose loop needs to be above that, and manufacturers usually specify a minimum height of around 600mm.
Raise and clip the hose.Route it up the back of the machine or up the cupboard side, and fix it there with a clip or the plastic hook usually supplied with the machine.
Check it is not pushed too far into a standpipe.The hose should hook loosely into a standpipe with an air gap around it. Pushed deep and sealed, the standpipe becomes part of the siphon.
Check the trap spigot connection.A hose clamped tightly onto a trap spigot is sealed by design, so the high loop is the only protection. This arrangement makes the loop essential rather than optional.
Test on a short cycle.Run a rinse or a short programme and watch the waste. No flow during fill means it is cured.
Suspect the machine if the loop is correct.If the hose is properly looped and clipped and it still empties while filling, the drain valve or pump may be stuck open, or the pressure switch may be misreading the level.
Check the machine is level.A machine tilted forwards can spill towards the drain path and confuse the level sensing. Level it on its adjustable feet.
Check the hose for splits.A split in the waste hose can let air in and change the flow behaviour, as well as leaking during pump-out.

Tips

Use the plastic hose hook supplied with the machine. It exists precisely to hold the high loop and is usually left in the box.
Clip the loop rather than relying on the hose's stiffness. Hoses relax and slide down over months.
If the machine was fine and started doing this after being moved, the hose has almost certainly dropped.

Common mistakes

Pushing the waste hose deep into the standpipe to stop it jumping out — It seals the pipe and turns the whole run into a siphon. The hose should hook loosely into the standpipe with air able to get past it.
Assuming a fill fault means the inlet valve — A machine siphoning out while it fills reports the same fault as one that is not filling. Watch the drain before ordering an inlet valve.

If it doesn't work

Water runs out during the fill

Cause: Siphoning through the waste hose — Fix: Raise the hose into a high loop above the drum and clip it.

Cycle takes hours or reports a fill error

Cause: Same — the machine never reaches level — Fix: Same fix; check the loop height against the manufacturer's figure.

Correct loop, still empties

Cause: Drain valve or pump stuck open, or pressure switch fault — Fix: An appliance engineer; the plumbing is not the problem.

Started after moving the machine

Cause: Hose dropped out of its loop — Fix: Reroute and clip the hose at the correct height.

Questions people ask

How high should a washing machine waste hose be?

The top of the loop should sit above the drum level, and manufacturers typically specify a minimum of about 600mm from the floor with a maximum too. Check the machine's own instructions.

Does a dishwasher need the same thing?

Yes. Dishwashers siphon in exactly the same way and need the same high loop, which is why both machines' instructions specify one.