What Causes Sewer Smells In Your Bathroom?

What Causes Sewer Smells In Your Bathroom?

How to get to the bottom of difficult to detect unpleasant odours

It’s one of the most annoying, frustrating and unpleasant experiences in the home – the pungent smell of sewers coming from the bathroom that no amount of disinfectant poured down the sink or the loo can shift. What can be causing it?

It could be one of various factors but fortunately most are easy to correct once found.

Driving you round the U-bend?

If the smell is literally driving you round the bend this could actually be a clue as to what’s wrong. The U-bend you can usually see below your sink (and there’s one serving the bath, shower and toilet) could be the culprit.

Some think the U-bend is simply there to prevent objects such as jewellery being flushed down the pipe. Whilst the U-bend can help here, its purpose is actually designed to stop sewer gases from reaching the room via the plug hole or pipe.

In normal operation the U-bend has water in it filled to a level that prevents gases that would be vent from the pipe that the sink, shower or other appliance connects to that leads up and out of your roof.

If the water has dropped to a level where gases can pass over it and up through the U-bend, or it’s evaporated completely, then unpleasant odours can result as gas is escaping into the bathroom space itself.

If your bathroom hasn’t been used in a while – perhaps you’ve been away or the odour is coming from a second bathroom not used in some time – and you notice a sewer-like smell then lack of water (or no water) in one or more U-bend could be the culprit.

Simply running some water from the sink, shower, bath and flushing the toilet will be enough to refill the U-bend and the smell will soon disappear.

Still smelling? It may be leaks or blockages

If the above doesn’t work or the odour is coming from a bathroom in regular use still check the above as some appliances may not be used as often as usual. For example, in the summer the bath may not get as much use as the shower does so water in its U-bend may have dispersed.

If the odour is still present, then check the U-bends for leaks; even a slow leak is enough for the water level in the U-bend to drop.

You may need professional plumbing services at this point if you can’t access some of the U-bends such as under the shower or bath.

There could be a blocked drain or pipe; the obvious tell-tale sign is slow draining water from the sink, shower or other. Basic drain unblocking methods such as using fluids or a plunger can be tried but, again, at this point you may need a plumber.

Checking the vent pipe

If the above have been investigated and the odour obstinately refuses to go, then there may be an obstruction to the vent pipe. As mentioned earlier, your bathroom appliances connect to this pipe that runs upwards usually out of the roof; waste gases go up this pipe to be vented outside.

The pipe could have become blocked by something like a bird nesting over it or some debris could have wedged inside it such as a piece of roof tile, or maybe snow and ice is causing an obstruction. This leaves the gases with nowhere to go but back through your bathroom.

A cracked vent pipe could be the cause but this would require expert investigation as to where the crack actually is; a call to a reputable plumber would definitely be required.

If you’ve recently had a bathroom reconfiguration and a sewer smell has appeared, then after checking the ‘water in the U-bend’ situation, investigate how the bathroom installers or plumbers have routed the vent pipe. If they’ve done a poor job this could be the cause.

Don’t suffer

Once you notice a sewer like smell, then it’s important to get to the bottom of it as sewer gases, along with being unpleasant, can be hazardous to health. If you can’t remove the smell yourself through the basic steps above, then be sure to call in professional plumbing help.


How to investigate and remove the source of unpleasant bathroom sewer odours from ensuring enough water is in the U-bend to checking the state of the vent pipe.





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