Water collects in dishwaser when it is not in use - why and how to stop?

[Lumo]

We have an Ikea dishwasher which works fine in that it fills, cleans and drains. However, when it is not in use, every so often the base fills with water which I assume is drain water somehow getting back into it. In the hot summer this gets rather unpleasant. The dishwaser connects to a drain which also has a sink and a washing machine connected. However, I cannot see a pattern to when the dishwasher fills, it does not always fill when the washing machine runs and does not always fill when the sink drains. It can go weeks without filling (when the sink and washing machine are used) then do it three days in a row.

What should I be looking for here? There is no U bend in the dishwasher drain (the washing machine has one) but I think I tried making one a few months back and it didn't seem to make a difference, but it could be I did it incorrectly. Apart from that I am pretty stuck for ideas. The kitchen drain itself is not blocked, a full sink empties very fast. Is there anything I can do to prevent this?

 

[Exedon]

Some clear pictures of waste pipework would be useful.

 

[Mottie]

Do you have a non-return valve fitted to the d/w drain pipe that may be occasionally being held open?

 

[Hugh Jaleak]

Difficult to say for sure without seeing the setup, but firstly, does the Dishwasher outlet hose rise right up to around the level of the top of the machine, before dropping to the drain? These machines are designed to pump the waste water out, so the drain hose must rise to prevent backflow into the machine when another appliance is discharged.

Secondly, how are the 3 appliances connected to the drain, a Photo would be immensely helpful here!

 

[Lumo]

Thanks for the replies. I will post a photo later. It's an Ikea drain with sink connected and below that the washing machine and dishwasher. I am pretty sure there are no non-return valves added to this.

The drain did not go to the height of the top of the machine, it just left the dishwasher, went behind the sink and then rose up to the drain level which is only about half way up the machine height. The original plumber did this. At some point I attached the pipe to the top of the cabinet at the height of the top of the dishwasher as I had a memory of seeing other setups like that and I wondered if the lack of that was causing the waste water to end up inside the dishwasher. However, after some time this came undone and the pipe fell back to the floor, but I just left it as that is how the plumber had done it so I thought it was probably OK. Could it be something as simple as that?

 

[Madrab]

If the DW drain pipe doesn't rise in a loop at least up above the level of its sink waste connection before dropping to the dishwasher, then yes, the waste sink water can run back down the drain pipe into the machine.

 

[JohnD]

Could it be something as simple as that?

Yes.

 

[gas112]

it could very well be the actual cold supply valve into the machine passing slightly with solenoid not fully shutting it off quite a common problem with washing machines etc .
is the water clear . is the water cloudy or smelly if left a couple of days

 

[Johntheo5]

I have a 7 year old Whirlpool D.washer and recently had to remove the drain hose to clean it out. There is a non return valve in the form of a rubber flap just where the hose attaches to the machine, hose clip keeps hose in place, had to turn machine on its side to remove.

Google your machine model and the NRV might look something like this (Whirlpool).

 

[Lumo]

Well I moved the drain pipe so that it rises up to the bottom of the counter top, runs along there, then goes down to the drain connection. So far so good, but it has only been a few days during which the machine was used and so pumping out anyway.

I'm pretty sure it is drain water collecting as it was not clean looking, but I suppose it could have been clean water which went bad over time.

Thanks for the replies and help.

 

[Min]

If that doesn't work, and the actual problem is the smell, rather than water being where it shouldn't be, then a couple of drops of teatree oil or a splash of white vinegar will kill the bacteria that cause the smell.
In the summer, sometimes my dishwasher smells (I only run it every two or three days). A generous dash of vinegar sorts it out

 

[Harkon321]

Mine did this and it was the dishwasher drain hose. It had been clipped up above the height of the sink waste. It had slipped off the clip and the sink waste was back filling down the pipe.