Slow drain toilet with old & new AAV but fine without

[OddJobRob]

Hi all,

Hope you're well.

Anyone any ideas... randomly 2 of our toilets started backing up when flushed (2 on same stack 1st floor and ground, 3rd loo (2nd floor) on its own seperate riser is fine) and takes circa 10s to level out.

When flushed you can hear the gurgles and burps from the basin/bath on 1st floor, so I thought it must be the AAV not opening and thus creating suction behind the flush.

Just put in a new AAV, but same thing happens. With no AAV, ie an open pipe, both toilets flush and drain normally.

Whats are the odds of the new AAV being faulty vs something else being the cause?

In my head it's not a blockage/restriction below ground floor entry or both loos would be restricted on an open pipe. Not a restriction between ground and 1st floor as the 1st floor would be OK with an open pipe but not 1st floor, and not restricted above 1st as it would work fine on an open pipe,but I'm no plumber!

All I can think of is that with the AAV installed, it's not generating sufficient suction to open the AAV, so is trickling away. How this can change when nothing has been done to the system, who knows, perhaps a leak which is allowing air in when vacuume is building? If so how the hell do I find it and fix it, all plumbing is concealed behind tiled walls etc.

Any ideas welcome, especially if it's something I can test/do without destroying the house 🤣

Cheers all

 

[snowhead]

It's partially blocked below the lowest W.C
It's nothing to do with the AAV.

I won't explain why, but as you have access to the AAV location.
Remove the AAV, cover the pipe end with cling film, get someone to flush either WC and watch what happens to the cling film, you'll see why it's not the AAV failing to let air in.

 

[Ben-gee]

The first thing to do in this situation is ALWAYS go outside and start lifting manhole covers. You will soon find out what’s going on and where to rod from.

 

[OddJobRob]

Many thanks both.

Pipe is blowing out on flush, so the volume isn't going down, it's going up and slowly down, makes sense, thanks Snowhead

Ben-gee, never noticed before but there are no covers in the grounds of the property, and non withing 25m of the front of house (backs onto other gardens and garages etc so cant check out back). Will see if anything in plans as to where the sewers run. As it stands, I can't find anywhere to inspect which seems very odd indeed 😬

 

[OddJobRob]

Assuming a blockage lower than ground floor toilet, is it worth trying to get a snake down the pan or does that carry little hope?

 

[Ben-gee]

My house was the same, previous owners had slabbed over two manholes when they did a “patio”!
I’ve redone all the drainage since and have four places to clear drains from ( touch wood I’ve never had to use any of them yet, but the more the better in my opinion.)

 

[OddJobRob]

Sorry all. Been a manic few days.

Thanks to all for their suggestions and inputs.

It was a restriction. I managed to find a single small cover, under a Bush in back garden. Had to cut a lot of Bush away, which had the strongest and hardest sharpest spikes I've seen outside South Africa, like nails!

Anyways, after a few piercings, got to cover (tiny one, was expecting a proper one 🙄) and there was a restriction at a y junction. Moved that and a large head of 'water' behind it took what felt like 30s to run through, was likely closer to 10.

So, appears that one leg of the y was fed by the 2 toilets at front of house, which were slow to drain as 'water' seeped past the restriction, which the 3rd loo at back of house entered via the other leg of the y, the straighter leg, and was flowing freely.

Twas true that with no AAV, air was pushed out the top of the pipe as the flush displaced air upwards as water wasn't going down fast enough.

Thanks all and happy flushing 😳