A few months ago my wife and I moved into a brand new house and soon noticed that there was a smell of drains in the ensuite bathroom. We called the builder who sent round the plumber but he seems quite clueless about most plumbing, it has taken him several attempts to fix various leaks and other issues and he seems to have no idea where the smell is coming from.
So I did my own investigations and found that if I covered over the shower drain the smell went away. I covered it with a piece of clingfilm and I could see the clingfilm move as air was moving in the pipe which lead me to the conclusion that the shower trap doesn't work. We have another one exactly the same in another shower although that one doesn't seem to smell, maybe because it is connected to the main soil stack (on a fairly long pipe) and the smelly ensuite is connected to a short stack with a drago (spelling?) valve on top?
Anyway I can't see how the shower trap can possibly work as it is because there is no standing water and air is able to flow straight through from the sewer!
This is the shower trap. Its basically a container about 80mm deep with an exit pipe about 10mm off the bottom, ie the trapped water will never be more than 10mm deep.
This is the cover, upside down, which is just a tube that sits in the trap. The tube was originally only 40mm long, not nearly long enough to reach the water level in the bottom of the trap. The tube is fixed to the cap so it can't be pushed any deeper into the trap. I extended it with a bit of yoghurt pot to make it 65mm, enough to reach the water level.
Trap with the cover fitted. Water flows down the inside of the tube attached to the cap.
A rather poor illustration. There is only a very small amount of water held in the trap because the exit pipe is so near the bottom. The cap fits into the hole and seals around the edge so the water has to go down the inner tube, but this tube doesn't reach the water so air is able to flow in from the sewer. I would expect the trap to be line a mini U-bend where the drain is sealed by a body of standing water, but its not (not without my mod).
This is what my modified trap looks like.
With my modification air is no longer able to flow through, the shower drains properly and there is no smell. But i shouldn't have to fix the shower drain with a yoghurt pot! What is wrong with it? The plumber thinks it was OK in the first place but it didn't work as a trap, only a drain. I shouldn't even have to do this, it should be the plumber's job, but it seems I have to tell him how to do his job! Unfortunately we seem to be stuck with this plumber because we have an NHBC guarantee on the house and this is the plumber that the builder uses.
I'm confused!
So I did my own investigations and found that if I covered over the shower drain the smell went away. I covered it with a piece of clingfilm and I could see the clingfilm move as air was moving in the pipe which lead me to the conclusion that the shower trap doesn't work. We have another one exactly the same in another shower although that one doesn't seem to smell, maybe because it is connected to the main soil stack (on a fairly long pipe) and the smelly ensuite is connected to a short stack with a drago (spelling?) valve on top?
Anyway I can't see how the shower trap can possibly work as it is because there is no standing water and air is able to flow straight through from the sewer!
This is the shower trap. Its basically a container about 80mm deep with an exit pipe about 10mm off the bottom, ie the trapped water will never be more than 10mm deep.
This is the cover, upside down, which is just a tube that sits in the trap. The tube was originally only 40mm long, not nearly long enough to reach the water level in the bottom of the trap. The tube is fixed to the cap so it can't be pushed any deeper into the trap. I extended it with a bit of yoghurt pot to make it 65mm, enough to reach the water level.
Trap with the cover fitted. Water flows down the inside of the tube attached to the cap.
A rather poor illustration. There is only a very small amount of water held in the trap because the exit pipe is so near the bottom. The cap fits into the hole and seals around the edge so the water has to go down the inner tube, but this tube doesn't reach the water so air is able to flow in from the sewer. I would expect the trap to be line a mini U-bend where the drain is sealed by a body of standing water, but its not (not without my mod).
This is what my modified trap looks like.
With my modification air is no longer able to flow through, the shower drains properly and there is no smell. But i shouldn't have to fix the shower drain with a yoghurt pot! What is wrong with it? The plumber thinks it was OK in the first place but it didn't work as a trap, only a drain. I shouldn't even have to do this, it should be the plumber's job, but it seems I have to tell him how to do his job! Unfortunately we seem to be stuck with this plumber because we have an NHBC guarantee on the house and this is the plumber that the builder uses.
I'm confused!
. An old traveller plumber like me would simply cut a Hep V O valve into the waste pipe run and leave the shower " drain " as it was without the yoghurt pot