Dishwasher drain blocked

[Terry Pinnell]

I'd appreciate some practical advice on how to clear a blockage in the outlet tube from our Bosch dishwasher please.

Evil smelling water remains after a wash. The filters and hole below them seem clear. As far as I can make out, waste is pumped out from below into a flexible hose that then comes up through the adjacent cupboard and connects to the side of the U-tube underneath the kitchen sink, as shown in this photo:

sink is draining fine, so it seems to me that the blockage must be somewhere in this tube. Without MAJOR hassle, or calling in a plumber, disconnecting it at the dishwasher itself is not an option. Which of the connections is best to remove: A, B or C? More to the point, what should I do once I've got access to that end?

Should I connect my garden hose somehow and force mains-pressured water down it?

How about pouring drain-cleaning stuff (caustic soda?) in?

Any advice would be much appreciated please.

[Bob Minchin]

You will have to make disconnecting at the dishwasher end into an option! remove hose completely and sort it out properly.

[Tabby]

Its not hard to do, just tip the machine over and undo the clip.

NT

[Bob Eager]

You can't, really. It isn't hard to do it at the other end, and wouldn't be a plumber's job anyway. Just take the side off the dishwasher. There may be a plastic clip (a sort of 'channel') that you have to prise off; it may break a lug or two (mine did) but there's an obvious place for a small bolt to be inserted when reassembling. The actual connection, once inside, is trivial.

[Peter Parry]

You may be lucky and the blockage is at B. If you remove at C and A and visually inspect the tube it may be there. Other common cause is thin bones getting past the filter and jamming the drain pump impeller. The drain pump has a very low starting power so can easily jam. Usually there is a fan on the other end which you can turn by hand once you tip the dishwasher up so you can check it.

[Terry Pinnell]

Bob (Eager), Peter:

Thanks both.

Further close examination appears to indicate that it's not a blockage in the dishwasher drain tube after all.

I hope I'm right, because I'm not at all confident about being able to slide out the dishwasher itself. When we had wood panel flooring installed, an 'edging strip' obstructs that. If it wasn't already obvious, I'm posting here as an inexperienced DIYer.

But I'll describe what I see as best I can and would appreciate confirmation of that please.

I'm trying to show is that the water that has drained from the sink (and dishwasher, and draining board) appears gradually to rise. So that eventually it reaches the level of the dishwasher outlet hose.

Yesterday I used a 'sink plunger' on the drain/filter hole of the dishwasher and put it through a couple of washing cycles while empty. That appeared to clear it fully. IOW, there was no water obvious at the base of the washing compartment.

But this morning there was. A lot, and foul smelling. That's what prompted me to closely examine the sink itself. After yet another pre-wash cycle I watched the water pumping out of its drain hose into a point a couple of inches above the top of the U-tube. After that had drained away, the water surface appeared to be where I would expect, i.e. at the top of the U-tube. But after 5 minutes or so it had risen as I described. So it would now be flowing back under gravity into the dishwasher.

I'm right, it's a complete mystery to me how this could happen! After the U-tube, the pipe goes drops gradually to a drain outside the house. As it happens (an unrelated issue) the vertical section of that pipe outside the house a few inches above the drain recently got broken, and I haven't yet fixed it, so I can see the sink water gushing out.

[Tabby]

Sounds like a partial block further down the system, somewhere after another appliance discharges into the pipework. A chemical cleaner may help clear it.

there's enough slack in the dishwasher drain pipe, just tying it higher up would prevent this backflow.

NT

[Terry Pinnell]

Thanks Tabby, much appreciate the fast reply. Your last point is a brilliant idea, despite its simplicity! There is in fact plenty of slack, so I've raised the hose so that its height is now an inch or two above the entrance into the sink drain.

Would you anticipate the pump having any difficulty with that slightly greater height?

Re the chemicals, I did in fact give it a couple of capfuls of sink cleaner this morning. Maybe that's contributed to the current status, which is: hot wash now finished, no water obvious in dishwasher, water surface in sink drain where it should be (inches below the 'flow-back' level).

That leaves the mystery of the rising level! Logic compelled me to think along same lines you described. But I can't think *what* other appliance could drain into that section. In a moment of madness I even went upstairs and ran sink and bath taps, but of course their waste doesn't emerge in that pipe. After the U-Tube, the plastic pipe just runs at a slight downward angle across the cupboard, makes a small dog-leg into the inaccessible corner unit, and then emerges from the outside wall 3 feet away.

BTW, I'm in the dog house now. I'd unscrewed the sink drain cover to get a better view down it. Then I decided I'd stick the rubber plug in and fill the sink in order to give it a thorough flushing out. Whereupon the cupboards and floor were immediately soaked before I got to the tap! Needless to say, my wife wasn't impressed!

[Skipweasel]

+1

Lift the incoming hose to make more of a hump before the connection to the drain.

[Mike Clarke]

Shouldn't be a problem. I'd raise it to be as high as possible, ours is only an inch or two below the underside of the worktop.

[Terry Pinnell]

Thanks both, done.

I'm still pondering over the mysterious rising level, but several hours on and haven't seen it repeated, so I'm optimistic! ;-)

[Tabby]

I'm not sure how much difference an inch would make, its not much.

no

If the drain cleaner has helped, I'd repeat it a few times to help clear it more.

NT