Strange sound when flushed the loo, followed by sewerage smell

Lulu58

Hi all, my husband just flushed the loo and it flushed as normal for a couple of seconds and then made an odd sound briefly which was like a roar.  The loo seemed to flush ok and there is/was a normal level of water in the pan.  A short while later there was a strong smell of sewerage coming from that bathroom which is still there.
The loo still flushes ok and there are no visible signs of water/sewerage escape but the pipework is hidden within a vanity unit.
Does anyone know what might have caused the noise and what is causing the bathroom to smell bad?

FreeBear

Might be time to lift a manhole outside and think about getting the drains rodded.

From time to time, I get odd noises from the loo, and it is usually an indication the drain is blocked.

Lulu58

Thanks, FreeBear.  We've had the drains rodded recently, but will get them checked again just in case.

Mickey666

Does the toilet connect to an external soil pipe that extends above the roof?  If not, there may be an 'air-admittance valve' (sometimes called a 'Durgo valve) somewhere inside the bathroom, probably hidden along with the pipework.  Sometimes these valve can fail but still 'flap about' making a peculiar noise.  Also, if they fail to close properly then smells from the sewer pipe can escape into the room.

Mutton_Geoff

I had a BTL flat that always had a whiff in the bathroom. When I ripped out the whole lot for refurb, I found the boxed in/concealed cistern had it's overflow pipe connected directly to a hole drilled in the soil stack which meant the stack vented into the top of the cistern and thus into the room. The ceiling vent fan was also tee'd into 2 other flats below so whenever they ran their fan, the exhaust entered the flat rather than venting out the longer pipe to the outside. A fan with self closing cover (Icon) sorted that out.

As suggested, could be a stuck durgo, especially if last flush contained a load of solids plus paper causing a 4" plug to go down the pipe sucking harder than normal (hence the noise).

Jeepers_Creepers

Lulu, why did you have the drains rodded recently?

As said above, the 'roar' was almost certainly a strong 'glugging-gurgling' caused by air being drawn down the toilet pan and pulsing around the U bend. And the smell afterwards most likely is due to not enough water remaining in the U bend to seal it off.

Do you understand what a U-bend does? 

The contents of the bowl go round this bend and then to a vertical soil stack. By the time it's plummeting down this stack, it's drawing quite a bit of 'suction' behind it. This is catered for usually by the stack continuing upwards to above roof eaves level where it's open to the air - so air can be easily drawn down there rather than your U-bend being sucked dry. So it's worth a quick glance at the stack top to see if a bird has made a nest on it... The other way to cater for this 'suction' is an air admittance valve (AAV) as explained earlier. This is used when you can't easily have a vent stack. 

It has a light flap inside it which allows air to be drawn in when required (during a flush), but closes off at all other times to block smells. 

First thing, then, is to see if you have a stack or an AAV. 

Lulu58

Mickey666 said:

Does the toilet connect to an external soil pipe that extends above the roof?  If not, there may be an 'air-admittance valve' (sometimes called a 'Durgo valve) somewhere inside the bathroom, probably hidden along with the pipework.  Sometimes these valve can fail but still 'flap about' making a peculiar noise.  Also, if they fail to close properly then smells from the sewer pipe can escape into the room.

Thanks for your post Mickey666.  The toilet connects to a large external soil pipe which is quite short in length, this then connects to the main downward soil pipe.  There is no durgo valve (had to look that up online!) that I can see.
Thankfully the smell has gone this morning and has not returned so I'm hoping it was just 'one of those things'. 

Lulu58

Sounds like you have a lot of issues in your bathroom, Mutton-Geoff. Hope you got them all sorted. 
I think the flush which caused the problem yesterday did contain solids and paper so hopefully that was the cause.  The smell has gone and we've had no repeat of it today.

Lulu58

Thanks for your reply, Jeepers_Creepers.  Very informative.
The drains were blocked and an investigation found tree roots which were cleared and the pipe sealed.
We have something which looks a bit like a small, pointy cage at the top of a pipe which I think is what you are referring to above.  There is no birds nest on top of it and it looks clear.  I can't see any AAVs.
As you may have seen from my other replies, thankfully there is no smell today.

Mickey666

If there’s no Durgo valve then Jeepers-creepers’ explanation seems most likely.  In the event of future ‘major’ flushes, perhaps check the water level in the pan afterwards.  If it looks too low,  therefore maybe not fully blocking air from the pipe work, a second flush should restore the correct level and prevent future smells.

Jeepers_Creepers

As Mickey says :-)