How to unblock a dishwasher that will not drain

What you need

• Cup or large sponge to bail water out of the tub
• Old towel and gloves
• Phillips screwdriver and Torx T20 for the pump cover on some models
• Torch
• Stanley knife for the spigot on the trap
• Old toothbrush for the filter
• Cleaning vinegar or dishwasher cleaner (Finish or Somat, 3-5 euros)
• Dishwasher regeneration salt (1-2 euros a kilo)
• 1.5 m dishwasher drain hose with elbow if the current one is split (10-15 euros at Leroy Merlin or Bricodepot)
• Kitchen sink trap with double spigot for dishwasher and washing machine if the current one has none (Jimten or Wirquin, 8-15 euros)

Step by step

1. 1

   Unplug and bail out the water

   Unplug the dishwasher or switch off its breaker. Take out the baskets and bail the water out of the bottom of the tub with the cup and sponge until it is dry. Lay the towel in front of the door.

2. 2

   Remove and clean the filter

   Turn the cylindrical filter in the base anticlockwise and lift it out together with the flat grille. Wash it under the tap with the toothbrush and washing-up liquid. Look into the recess it sits in: there is usually food debris and glass in the bottom.

3. 3

   Open the pump cover and turn the impeller

   Under the filter there is a round or half-round cover: turn it a quarter turn or release the clip (some models have a Torx screw). With the torch, look at the impeller and turn it with a finger. Remove any glass, pips, bones or bits of label jamming it. It should turn freely with slight resistance.

4. 4

   Check the drain hose

   Pull the dishwasher out of its housing if needed and follow the hose to the kitchen sink trap. Look for kinks, crushing by the unit or the plinth, and check that it rises to at least 50 cm before dropping down to the spigot (the high loop stops dirty water flowing back).

5. 5

   Check the spigot on the kitchen sink trap

   Disconnect the hose from the side spigot on the trap. If the spigot still has an uncut blanking cap, cut it off with the knife. If it is full of grease, clean it out with a stick and hot water. Reconnect with the clip done up tight.

6. 6

   Reassemble and run a drain test

   Close the pump cover, refit the filter, plug in and start a short programme or the drain function. Listen to the pump: it should run steadily, with no dry humming, and the tub should be empty at the end.

7. 7

   Vinegar cleaning cycle

   Put half a litre of vinegar in a bowl in the top basket and run an empty programme at 60-65 degrees. Top up the regeneration salt and set the water hardness to the high level in the machine's menu.

Why a dishwasher will not drain: the 4 points to check

Water leaves a dishwasher along this route: bottom of the tub, filter (a fine mesh cylinder with a flat grille around it), drain pump (under a cover in the base, with a plastic impeller), drain hose coming out of the back of the machine, and the spigot on the kitchen sink trap or a wall connector. A blockage at any of the four leaves dirty water in the tub at the end of the cycle, and each one has its own symptom.

If the filter is full of food debris, the water drains slowly and the dishes come out gritty; this is the most common cause and the easiest. If the pump impeller is jammed by a piece of glass, an olive stone or a bit of label, the dishwasher hums at the end of the cycle and pumps out nothing. If the hose is kinked or crushed by the kitchen unit, the fault appears after moving the machine or after a kitchen refit. And if the spigot on the sink trap is blocked, water comes up into the kitchen sink when the dishwasher drains, or flows back dirty into the tub.

There is one case we see in newly fitted kitchens: the installer connected the hose to the side spigot on the sink trap but never cut the blanking cap off that spigot. The dishwasher manages two or three cycles thanks to the hose, then starts holding water. It is solved by cutting the cap off the spigot with a Stanley knife, five minutes.

• Drains slowly, gritty dishes: dirty filter.
• Hums at the end of the cycle, pumps no water: jammed pump impeller.
• Fault after moving the machine or refitting the kitchen: kinked hose or spigot on the trap not cut open.
• Water comes up into the kitchen sink when it drains: blockage in the sink trap or the pipe in the wall.

Mistakes when unblocking a dishwasher: chemicals, the pump and diagnosis

The first is pouring chemical drain unblocker into the tub. It never reaches the pump, sits in the bottom, attacks the rubber seals and leaves residue on the dishes in the next cycle. Dishwashers are not unblocked with chemicals; they are cleaned by hand. At most, a cycle with vinegar or a dishwasher cleaner once the blockage is sorted.

The second is putting your hand in the pump with the machine plugged in. The impeller can start up and, although it is plastic, it cuts. Unplug the machine or switch off its breaker at the consumer unit before removing the pump cover. The third is forcing the pump cover: on most models (Bosch, Siemens, Balay, Beko) it turns a quarter turn and has a clip or a tab; if you pull without turning, it breaks.

And the fourth is replacing the drain pump when the problem is in the kitchen drain. If the kitchen sink is also slow, or if water comes up into the sink when the dishwasher drains, the appliance is fine: the blockage is in the sink trap or the pipe in the wall. Before buying anything, fill the sink and let it empty in one go.

When to call a professional

If the filter and impeller are clean, the hose is not kinked and the spigot on the trap is open, but water still sits in the tub, the drain pump has failed and needs replacing (30-60 euros for the part plus labour), or the control board is not switching it on. That is a job for an appliance engineer, not for us. What we do handle is everything after the hose: the kitchen sink trap, the pipe in the wall and the kitchen branch pipe.

When the kitchen sink and the dishwasher fail at the same time, unblocking the kitchen drain costs 70-120 euros including the call-out, and 110-180 euros if there is grease in the pipe in the wall and we have to run the drain machine. Prices in how much drain unblocking costs and the service in drain unblocking. If the spigot on the trap is broken or the trap is an old one with no dishwasher connection, our plumber swaps it for one with a double spigot on the same visit for 15-25 euros in materials.

We arrive in 20-45 minutes in Valencia, Alicante, Torrevieja and Benidorm. Local pages: drain unblocking in Valencia and in Alicante.

Limescale and dishwashers on the coast: hard water is the enemy

With the water in Alicante and Valencia, at 40-50 French degrees of hardness, a dishwasher without regeneration salt builds up limescale on the filter, the pump impeller and the non-return valve in the hose in under a year. A scaled-up impeller turns stiffly, the pump overheats and eventually fails. Keep the salt reservoir full (dishwasher salt, 1-2 euros a kilo), set the water hardness in the machine's menu to the high setting, and run an empty cycle with a descaler or half a litre of vinegar every two months.

In homes that are shut up for half the year, the water left in the pump sump evaporates and the food residue dries out and jams the impeller. Before closing up, run a short empty cycle, take out and clean the filter, and leave the door ajar. When you come back, the first thing is a vinegar cycle before loading any dishes.

Related guides

If the kitchen sink also drains badly, the problem is shared and you solve it with how to unblock a kitchen sink. If the blockage resists everything, how to clear a badly blocked pipe. And for monthly maintenance of the kitchen drain, baking soda and vinegar for blocked drains.