Waste coming back into toilet

[jamiemcd]

Hi,
I'm hoping someone can help. I moved into a house about 6 months ago now, and when one of the two upstairs toilets is flushed, some waste back-fills into the other one and vice versa. There is another downstairs toilet in the house that is completely unaffected, and nothing else seems to be affected (doesn't fill into bath or shower etc.). When I flush either toilet, some small bubbles come back up in the bowl.

I've tried snaking the toilets but there doesn't appear to be a blockage (at least as far as the snake will reach...). The soil stack appears to vent into the loft space and it has an Air Admittance Valve fitted to it. The loft space is relatively well ventilated.

Does this sound like anything anyone has come across, and does anyone have any ideas as to what to do to investigate/fix it?

Thanks for any help anyone can provide!

 

[mountainman]

Could be a poor soil pipework configuration.
Bear in mind that an AAV allows air into the soil stack for ventilation purposes, it won't let pressure in the stack out.
You may be creating pressure in the stack that can only be relieved by backflow into the other toilet.

 

[jamiemcd]

Thanks MountainMan! The problem is there with and without the AAV unfortunately, and I only really fitted it as there was an unpleasant smell in the loft space on still days...

I guess there is probably no solution for a poor pipework configuration? Is it worth/a good idea to spray water down the soil stack vent pipe with a garden hose to clear any blockages there?

 

[mountainman]

You could well have a restriction causing the problem.
Probably the easiest way to check is to get a camera survey done.
Not cheap to do it properly but worth the cost.
One of the forum members will probably be able to help you out if you post your location.

 

[snowhead]

There's a partial blockage after the 2 W.c's join the stack.

Is it a straight drop form the pipe end in the loft, maybe rod down?

The stack shouldn't vent to the loft it should have been thro' the roof.
The blockage is causing the smell, and the open vent in the loft was letting it in.

The AAV has just masked the problem.

 

[Dotty]

Do these two toilets sit back to back? McAlpine do a pan connector with a non return flap which would prevent this problem reoccurring. But check for a blockage first.

 

[jamiemcd]

Hi guys,
Thanks for all the very quick replies - very impressed!

I've just been up to the loft and done a bit of an investigation. Turns out that the stack DID exit through the roof but the pipe that connected a rectangular fitting in the roof had fallen off. I hadn't seen it previously lying in the insulation, and had fitted the AAV. My fault on that one!

So, I tried snaking the vent pipe but either there was no blockage or the snake wasn't long enough! (It's got a 2-3 foot horizontal section on the end of it so I don't think it got very far...). I've ran a reasonable-pressure garden hose down both toilets and the vent stack for a couple of minutes each. Difficult really to tell the results, but hopefully any minimal blockages that have been affected the pressure will have been cleared. There's certainly no water clearly backing up.

Croppie - they are almost back-to-back...offset by maybe two feet or so. Unfortunately they're both totally boxed in so it's difficult to tell what's in there!

 

[brasso1981]

Yes the non return thing is also to stop rodents entering houses. We used one a few years ago on a barn conversion with two toilets backing on to each other.

 

[snowhead]

An idea to shift it if it is partly blocked.

Using 2 people and 2 buckets of water.

1 person in each W.C, flush then drop the bucket of water in as well, both w.c at the same time, you'll have to knock on the wall to get co-ordination.