Trying to Understand my Waste and Soil Pipe Plumbing

[endaxi]

Hi,

Having recently started another thread here https://www.diynot.com/diy/threads/occasional-unwanted-odour.578145/ I have done some investigation, and armed with better knowledge I thought I'd seek your help on this thread.

I have a main bathroom at the front of the house upstairs which has a boxed-in internal soil pipe running down through a downstairs cloakroom/WC and up into the loft where I can now see it is vented through the roof.

I also have two small en-suites shower rooms next to each other at the back of the house upstairs, one of which has an internal soil pipe. Presumably the other shower room's waste feeds into this stack too. This soil pipe goes into the loft and terminates. I thought it had an Air Admittance Valve capping it but closer inspection showed it to be just a polystyrene cap.

As the back stack appears to be unvented I would like to know if it is connected to the front stack by some kind of vent pipe.

I can find no such connecting pipe in the loft so am wondering if there is likely to be one under the upstairs floorboards.

If so, this may be the root cause of an intermittent sewage odour that seems to linger along the likely route of the connecting pipe.

Sorry for two threads but I'm keen to understand what may be happening before I call in the drainage experts.

Many thanks.

 

[Bodd]

Can you not take the vent through the roof?

 

[endaxi]

Hi Bodd, thanks for posting. The house is nearly 20 years old and the problem has just occurred. I'm just trying to find out how things are plumbed so as to understand what may have gone wrong and how it can be fixed.

 

[Bodd]

Hi Bodd, thanks for posting. The house is nearly 20 years old and the problem has just occurred. I'm just trying to find out how things are plumbed so as to understand what may have gone wrong and how it can be fixed.

If you have an air admittance valve in the loft then this could be stuck.

 

[Deleted member 267285]

If it’s just a polystyrene cap, then this won’t be airtight, allowing odours back in, however if the issue has just occurred, then it might be that the aav has come off,iirc, some are fitted with polystyrene to prevent freezing.

 

[endaxi]

Thanks for the replies guys.

The stack at the back of the house that terminates in the loft and has a polystyrene cap is tricky to get to. Before I go back into the loft to see if there's an AAV under the polystyrene cover I'd like to be fairly sure that fitting a new valve will cure my problem.

There is no gurgling sound from sink drains and the odour is normally in the bedroom and landing as opposed to in the bathrooms. I would have expected the odour to come from a sink drain or something and for there to be some gurgling noises in the sink when the toilet is flushed if the AAV was sticking. Any thoughts?

The new AAVs I've looked at don't seem to have these polystyrene covers so maybe the design has improved over the years. Some are good to operate between -20 and +60 degrees.

Floplast recommend their valves are serviced every year. If I do have one under that polystyrene cover then it hasn't been touched for nearly 20 years so it could probably do with changing by now whatever. I just hope it's a push fit and not glued.

 

[denso13]

Before I go back into the loft to see if there's an AAV under the polystyrene cover

AAV's subject to freezing should be insulated, and this could be a polystyrene cover. I'll suspect you'll find that's what you have.

 

[endaxi]

AAV's subject to freezing should be insulated, and this could be a polystyrene cover. I'll suspect you'll find that's what you have.

Yes, CBW suggested that earlier and I think you're correct. I've just bought one that doesn't need a polystyrene cover and also a little can of silicone aerosol to help fit it. I'm going to collect a few loft boards to use as crawl boards later to see if I can get close enough to the top of the stack inside the loft. As long as the existing AAV isn't solvent welded onto the pipe then I might just get the job done with a bit of luck and a following draught.

 

[endaxi]

Oh well, I put some boards down and got myself right to the top of the stack. As you guys suggested the AAV was under the polystyrene cap. I tried to turn it but couldn't, so guess it's glued on... No luck and a following draught then haha.

The soil pipe comes into the loft then into a 90 degree elbow and a short length of horizontal pipe to bring it further in (thankfully), then into another 90 degree elbow to turn it upwards again. The AAV looks like it's stuck straight onto the elbow. At this point I start to get cold feet and think I should perhaps get a plumber in. I said as much to my wife and she let out a sigh of relief... no faith in me then

I have a Polyvalve SPV110 currently fitted and have bought a FloPlast AF110 Push Fit. It looks a bit different but most reviews are good. I don't know a good one from a bad one to be honest. From what I can see I just need to get a new 90 degree elbow and swap out the old elbow and AAV with the new elbow and AAV.

There's been no odour for about four days now so perhaps something's righted itself. I don't know if AAVs just fail or if they become temperamental for a bit first. I'll sit tight and see what happens. As soon as I get a whiff again I'll get a plumber to to fit a new elbow and AAV. As straightforward as it appears, I know from experience that things can go wrong when DIYing, so I'll leave it to a professional and keep the smile on my wife's face

As an aside, if you haven't lost the will to live yet, we also get intermittent odours from a round drain cover just outside our downstairs loo. I thought about using some manhole cover sealing grease but it comes in a great big expensive tin. If I just used some Vaseline or something and fill the gaps without even taking the cover off would that stop the odours getting through?

Many thanks. I do appreciate all the help I get on here from you guys giving your time and sharing your expertise.

 

[Deleted member 267285]

If there’s been no odour for 4 days, and no odour when you entered the loft, if could suggest something else. As the phrase goes “if it isn’t broke, don’t fix it”. As for the drain cover outside, is this a manhole cover, inspection chamber type or gulley cover?

 

[endaxi]

If there’s been no odour for 4 days, and no odour when you entered the loft, if could suggest something else. As the phrase goes “if it isn’t broke, don’t fix it”. As for the drain cover outside, is this a manhole cover, inspection chamber type or gulley cover?

The cover is about 13 inches in diameter and has a look of smooth cement. It's got a recess in the middle with a metal bar to use as a handle. It's about a foot from the outside wall of our downstairs loo and is elevated. We get occasional odours in the downstairs loo but as it's been confined to that one room we've just lived with it and used bleach and air fresheners.

It's only since I've been researching odours due to our recent problem that I've re-visited this old issue and thought about this cover. There is an airbrick in the wall (about a foot from the cover) and now I'm putting two and two together and realising that the odour we get in the downstairs loo is probably related to the odour we get outside and it's probably coming from this cover and then going in through the airbrick.

So, I thought if I could seal the cover with grease I might get rid of the occasional outside odour and the inside odour in one swoop. I should mention we are on a slight incline and the houses below us have a pumping system that pumps waste up the hill to then be carried away by gravity. That's as I understand it anyway. If the pump just pumps as and when needed then then that could explain an intermittent odour coming from the drain cover I thought.

 

[Deleted member 267285]

Sounds like an inspection chamber cover or rodding eye (although possibly too big).

 

[endaxi]

Sounds like an inspection chamber cover or rodding eye (although possibly too big).

It's in line with the soil stack so inspection chamber cover sounds about right. I don't think there's any pressure behind it so I'll give the Vaseline a go for a start.

 

[Deleted member 267285]

I’d try and lift if first, see if it’s sat right.

 

[endaxi]

It looks seated and I've had a fair-sized plant pot on it for years holding it down but I'll have a go.