Sewer gas smell in bathroom

G

groober

Guest
Two plumbers have been unable to explain the reason for this problem to me so, I am posting here on the off chance that someone has had a similar problem.

Scenario:
External vented stack for upstairs toilet replaced by internal unvented stack (extension added to house). While the stack is not vented directly, there is a vent on the sewer at the start of the run (we are first house in a terrace and at the start of the run).

Slight but noticeable sewer gasses are escaping into the bathroom now.
The sink and bath both run off to an external hopper so the toilet is the only thing using the 4 inch pipe.

There are no water leaks around the bowl or where the toilet joins the 4 inch. Nor is there a leak at the base of the internal boxed off area where the 4 inch enters the sewer (this is in a downstairs utility room).

The smell in the bathroom can be gotten from the water in the bowl and the cistern (it's a new toilet). The water trap appears to be fine (observed by both plumbers). When the toilet is flushed the water is never sucked out of the trap. On the contrary, the water level in the bowl rises slightly but not excessively.

There is a downstairs toilet Y-ing into the same sewer and there are no problems with smells here.

Due to the extension work being completed, there is no opportunity at this stage to vent the stack above the toilet. The only option available is to T into the internal 4 inch (by external wall) and create a vent out from there. Both plumbers agree that this is worth doing but cannot guarantee it will solve the problem due to the toilet being above the proposed vent.

Questions:
1. Does anyone recognise this problem?
2. Is it possible that the toilet itself could be at fault (dual flush)?

I will probably post this elsewhere also.
Any help greatly appreciated.
 
groober said:
The smell in the bathroom can be gotten from the water in the bowl and the cistern (it's a new toilet)..
Click to expand...

This is very strange, the water in the cistern should not have a smell from it. Is it being fed from a tank? If so, check the tank to see if there is a smell from it.
 
The tank is fine. The cistern smell could possibly be explained by the overflow pipe taking in air from the bowl. I'm explaining this badly but ultimately there is not a problem with the water itself. It is pumped from a sealed aqua-box.
 
nine times of of ten it is coming from a bad seal where the toilet connects to the white fitting(with black rubber) at the rear. It may be water tight but not air tight.

The vent can be reduced to 1 1/4 inch pipe and ran at high level, is this possible?
 
Davy Jones is right. Check the flexible pan connector where the toilet connects to the sewer pipe. It is not uncommon for sewer gases to escape from this connection as some pan connectors were very loose fitting.
I have also heard of problems in the area where the WC Pan connects to the WC cistern. It seems that with some styles of sanitary ware there has been problems with the escape of sewer gas from this area due to faulty seals.
I know that you can have problems with certain types of Dual Siphonic WC suites.
 
It certainly could be the toilets themselves,as this happened to my brother on a new build.If you search for username davcot you will see the post.
 
Yeah, the plan was to put in a reduced width vent. It will exit a downstairs wall and extend over the gutter of the single story extension. It will 3 metres or so off the ground and 1 metre from any existing or neighbouring openings.

I will check the connection to the 4 inch, the davcot posts and the possibility of the pan-cistern connection being a problem.

Thanks so far.
 
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