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Discuss Dishwasher suddenly not draining past the u-bend in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

F

Fullpint

Hi - First time poster, hope you can help.

My dishwasher has been in place for about two years and has not had a problem until a few days ago, when I found the dishes in the cupboard full of water.

I emptied the cupboard and turned the dishwasher on, expecting a leak in the hose or the drain pipe. But no - water was gushing out of the grey polypipe and shooting up past the inserted hose.

I checked the u-bend and it's clear. I put a drain snake down and got about 4m in, all ok.

If I take the U-bend off (all the white stuff in the image) and put the dishwasher drain in the end of the grey pipe, it all works fine.

As soon as I put the u-bend back on, water gushes up again. It's like the pump is pumping too hard and the water hits the u-bend too fast and shoots back up.

The pipe is definitely clear as I have poured water in and it never backs up. Not sure what to do now. Thanks for any help.

Image:
Imgur

https://PLACE IMAGES DIRECTLY INTO POST - CLICK UPLOAD OR COPY AND PASTE THEM INTO THE POST. IMGUR IS BLOCKED./a/0sTaR72 Imgur

IMG_8257.JPG
 
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rpm

Esteemed
Plumber
Surprised that has worked tbh. Something has changed if you say it worked ok for two years so put thinking cap on.
 
OP
F

Fullpint

Surprised that has worked tbh. Something has changed if you say it worked ok for two years so put thinking cap on.
It's actually worked for 7 years. New dishwasher 2 years ago. What is surprising about that set up? It was like that when I moved in.
 
OP
S

Sharp Point

There could be a few reasons why it’s not working.

The drainage pipe from the washer could be full of gunk round the inside of the pipe, this could cause the velocity of the water to speed up and hit the bottom of the u bend and bounce out. The trap could be on a run that has a air admittance valve and that’s stuck and causing a pressure build up in the waste pipes and not allowing the water to flow. The pump could on its way out and for some unknown reason running to fast. There’s still a blockage in the main pipe, yes you said you put a snake down.. but it could’ve slipped down through the 15mm orifice that’s left through it, from hard baked fat/ grease/ soap build up.

Take your pick, it’s one of those
 

rpm

Esteemed
Plumber
There could be a few reasons why it’s not working.

The drainage pipe from the washer could be full of gunk round the inside of the pipe, this could cause the velocity of the water to speed up and hit the bottom of the u bend and bounce out. The trap could be on a run that has a air admittance valve and that’s stuck and causing a pressure build up in the waste pipes and not allowing the water to flow. The pump could on its way out and for some unknown reason running to fast. There’s still a blockage in the main pipe, yes you said you put a snake down.. but it could’ve slipped down through the 15mm orifice that’s left through it, from hard baked fat/ grease/ soap build up.

Take your pick, it’s one of those
Pump running too fast ? Don`t think they are variable speed. ;)
 
OP
F

Fullpint

There could be a few reasons why it’s not working.

The drainage pipe from the washer could be full of gunk round the inside of the pipe, this could cause the velocity of the water to speed up and hit the bottom of the u bend and bounce out. The trap could be on a run that has a air admittance valve and that’s stuck and causing a pressure build up in the waste pipes and not allowing the water to flow. The pump could on its way out and for some unknown reason running to fast. There’s still a blockage in the main pipe, yes you said you put a snake down.. but it could’ve slipped down through the 15mm orifice that’s left through it, from hard baked fat/ grease/ soap build up.

Take your pick, it’s one of those
Thanks, yeah I know you're right. It's got to be one of those.

The weird thing is it all works fine if I remove the u-bend and hold the washer drain pipe in the grey down pipe.

Would you recommend putting the snake into the washer drain pipe?!
 
OP
S

Sharp Point

Pump running too fast ? Don`t think they are variable speed. ;)

If they’re a lower voltage than 240 and the board is failing, there is a possibility of them running faster due to over voltage
 
OP
F

Fullpint

Good, do you know what a manhole looks like? On the understanding that even if you don`t St. Google will show you I suggest you go and lift yours. ;)
I'm on the 7th floor, so if my manhole was blocked there would be bigger problems!
 
OP
S

Sharp Point

Is the main stack( about 4” in diameter) plastic or cast iron?
 
OP
S

Sharp Point

I’d be inclined to disconnect that waste pipe run all the way back to the connector on the cast and flush/ clean it out. Make a physical effort to make sure the fast pipe isn’t corroded to the point of blocking the pipe.
 
OP
F

Fullpint

I’d be inclined to disconnect that waste pipe run all the way back to the connector on the cast and flush/ clean it out. Make a physical effort to make sure the fast pipe isn’t corroded to the point of blocking the pipe.
That would mean pulling the kitchen apart, which I'm not keen to do! Looks like I'll have to get someone in. Thanks for the suggestions, you've been very helpful.
 
OP
S

Sharp Point

That would mean pulling the kitchen apart, which I'm not keen to do! Looks like I'll have to get someone in. Thanks for the suggestions, you've been very helpful.
Sometimes that’s what’s involved, welcome to our world
 
OP
F

Fullpint

I’d be inclined to disconnect that waste pipe run all the way back to the connector on the cast and flush/ clean it out. Make a physical effort to make sure the fast pipe isn’t corroded to the point of blocking the pipe.
I ran the dishwasher drain through the u-bend so that it feeds directly into the down pipe (after the u-bend). I'm going to guess that's not best practice! But, I've run two dishwasher cycles without issue. Does that help narrow it down? It can be a blocked drain? It must be something to do with the pressure the washer is draining at?
 

rpm

Esteemed
Plumber
I ran the dishwasher drain through the u-bend so that it feeds directly into the down pipe (after the u-bend). I'm going to guess that's not best practice! But, I've run two dishwasher cycles without issue. Does that help narrow it down? It can be a blocked drain? It must be something to do with the pressure the washer is draining at?
That is half of it. You`ve had the answers both in writing and pictures on page1.
Goodnight.
 
OP
F

Fullpint

That is half of it. You`ve had the answers both in writing and pictures on page1.
Goodnight.
Well, I came here for help. I found one guy that tried, and I also found a sanctimonious prick. You know the answer.
 

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