Bosch - Drains and then backfills

[WoodleySaint]

We have a Bosch dishwasher which, at the end of a cycle, drains fine. However, for some reason, after a few hours, it back fills so that it full with the murky water it has just pumped out.

There is a kind of plastic water matrix which fresh water gets pumped into and the dirty water out of, which has a float in the top. I took this off and cleaned it as best I could but this did not resolve the matter.

Does anyone have a clue why it would do this?

Any help would be much appreciated.

WoodleySaint

 

[JohnD]

Is the waste pipe attached to the trap on your kitchen sink?

 

[WoodleySaint]

Yes, it is attached to the trap on the sink.

 

[JohnD]

Then I expect the dirty water from the sink is running down the wastepipe into the dishwasher.

Look at the pipe run. It needs to rise up in a curve so that the top of the curve is higher than the trap (and preferably up against the bottom of the draining board so that it is higher than the water level in the sink).

 

[WoodleySaint]

Thanks JohnD. The curve of the waste pipe is higher than the sink trap but is a few inches lower than the drainer height. I'll re position it this evening.

Is there a valve which should prevent the back filling from happening? It looks like the float mechanism in the 'plastic water matrix' should have something to do with this?

Thanks again

WoodleySaint

 

[JohnD]

Not that I know of. As an experiment, you could fill the sink with clean water with some colouring in it (like food dye for cake icing) and pull the plug out. With the dishwasher door open you may see it running in.

p.s. if you have a washing machine connected to the same trap, the dirty water might be coming from there.