Kitchen sink airlocked

[TomSandy]

Hello, My one and half bowl kitchen sink drain seems to be airlocked or blocked, not sure. I've P traps installed, I've to constantly open air vent valve to let water drain. When I open the air valve water drain freely so may be it's not blocked but air locked? I'm attaching image. Any suggestion on how to fix it.

The McAlpine P trap's air vent is suppose to open up automatically if airlocked?

 

[Deleted member 120897]

Does this happen on both bowls? Is it a case of water won’t go down, or takes an age?

 

[TomSandy]

Does this happen on both bowls? Is it a case of water won’t go down, or takes an age?

Yes it happens to both bowls.

I've been dumping soda+vinegar and flushing with hot water, it works for few hours then again block develops. Opening P trap's air vent works and water flows freely. It does suggest that there is air lock somewhere for sure. Kitchen is on the ground floor. There is no issue with draining anywhere else in the house. Lifted manhole cover and checked, it's all clear. no issue with toilet drainage. There is no foul smell.

Another issue is that I can't locate AAV. The kitchen and a shower room+toilet is built as extension. I've been in the loft above kitchen, didn't see any AAV. Haven't looked loft above shower room as it has very narrow access, could it be there? Where would you normally install it?

I've bought snake so I'll give it a try tomorrow. I'm been flushing out soda+vinegar too quickly so thinking of doing it once more and leaving it overnight before flushing.

I've read a lot of threads on this forum but can't figure out anything else to do except jetting which is my last resort. I'm also hesitating jetting as I've only access to 1.7" PVC pipe which you can see in the image, not sure if I jet it inside it? I don't think it will work as it has 90 degree bend. I don't have access to main (bigger) drainage pipe from anywhere else. I don't want to cut PVC pipe as I'll make a mess of it.

Anything else to try?

 

[TomSandy]

I'm done with soda vinegar, it didn't help at all.

I've ordered mcalpine ventapipe VP3.

I was wondering if this will help?

 

[snowhead]

The Ventapipe won't fix it.

There's a blockage (almost total) downstream, possibly behind the board with the socket on where the pipe has an elbow to go out through the wall or where it drops into the floor/ joins other pipework.

There may be an access point behind the board to use the snake in or if not take the left trap off and push the snake down from there.

When the water starts to flow keep twisting the snake around and run water down to clear the blockage (grease) off the internal sides of the pipe.
If it is grease the snake will push through it and when pulled back the hole in the blockage will close up again.

The P trap vents are to let air in to break a syphon caused by flow past the end of the pipe lower down.
The Ventapipe does the same thing.
What you are doing by releasing the vents is to let trapped air out and allowing the water to drain out through a very small hole in the blockage.

Using any chemicals on the blockage is only removing a very small amount of it, hence why the water stops running away

 

[TomSandy]

The Ventapipe won't fix it.

There's a blockage (almost total) downstream, possibly behind the board with the socket on where the pipe has an elbow to go out through the wall or where it drops into the floor/ joins other pipework.

There may be an access point behind the board to use the snake in or if not take the left trap off and push the snake down from there.

When the water starts to flow keep twisting the snake around and run water down to clear the blockage (grease) off the internal sides of the pipe.
If it is grease the snake will push through it and when pulled back the hole in the blockage will close up again.

The P trap vents are to let air in to break a syphon caused by flow past the end of the pipe lower down.
The Ventapipe does the same thing.
What you are doing by releasing the vents is to let trapped air out and allowing the water to drain out through a very small hole in the blockage.

Using any chemicals on the blockage is only removing a very small amount of it, hence why the water stops running away

Thanks for such a clear and detailed explanation.
I did give snake a go and pushed it as far as I can before sort of hitting some block (may be another bend). Didn't want to apply brute force. It seems to have cleared pipe a bit and water flows freely now. Let's see how long it last.

Next time I'll remove board and will have a look what is behind it and try snake again.

 

[TomSandy]

So one more effort. Removed the plywood, checked behind and all I could see was this 1.5" pipe only so I'm not sure where exactly it connects to the main, may be somewhere underfloor. I just tried 7m snake, no debris came out when I pulled it back. Problem persists. What is next? Try longer snake? How long?