Sewer gas smell from cold water tap

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Granger

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Our house in on the town sewer and water. After about 5-6 hours or so of not using the cold water taps in our upstairs master bathroom, when we first open the taps they smell of rotten eggs. Both his and hers taps. This also happens in our upstairs guest casita. I’ve tried pouring boiling water and vinegar down the pipes. I can’t figure out why the cold water taps have this smell. The drains drain very well and I’ve cleaned out both p traps. We do have a hot water recirculating system and sometimes the cold water comes out a little warm for some reason. Also all of the downstairs bathrooms do not have this problem so gas is somehow building up and rising into the upstairs plumbing.
Any ideas?
 

Reach4

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Interesting. I would turn off the recirculation pump for a couple days, and see if that changes the symptoms.
 

Bigealta

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I get that in a rental with a well. I use hydrogen peroxide to Clean the water lines. I have a small house filter that I take the filter out and pour in about 16 oz or so of hydrogen peroxide. Then just open the taps a bit to get it into the lines. let sit for an hour or so. Then flush out by opening taps. Works great for my rotten egg smell.
 

Granger

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I get that in a rental with a well. I use hydrogen peroxide to Clean the water lines. I have a small house filter that I take the filter out and pour in about 16 oz or so of hydrogen peroxide. Then just open the taps a bit to get it into the lines. let sit for an hour or so. Then flush out by opening taps. Works great for my rotten egg smell.
I’ll try both - worth a shot thanks!
 

Master Plumber Mark

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You need to be more specific.... odds are that the rotten egg smell is coming from your hot water side of the faucet.....

if it has a rotten egg smell it most likely is coming from the anode rod breaking down in your water heater..

you either need to remove the anode rod from the heater and see what it does
or you need a new water heater depending on the age
 

Jeff H Young

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Agree with coming from water heater but he was specific on stating from cold water side . Could be wrong info or some how gasses go up and out cold side . But sounds classic to me w/h anode
 

Granger

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agree with coming from water heater but he was specific on stating from cold water side . could be wrong info or some how gasses go up and out cold side . but sounds classic to me w/h anode
Thanks for the replies. Water heater is 6 years old. I’ll see if I can remove it but it might be stuck in there. I turned off the recirc pump so if the smell abates then it was the heater? Smell is only out of the cold side taps on the sinks. Not the shower.

Thanks
 

Reach4

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If you could check for residual chlorine when you run the taps, and found no residual chlorine, I would try sanitizing the pipes.

So if turning off recirc stops the H2S in the cold, then I would tend to think WH. And then some mechanism that I don't understand selectively moves the smell to the cold.

If turning off recirc does not change the symptoms, I would consider sanitizing the plumbing. If you want to get into that, we can discuss techniques. Do you know if you have old-timey water hammer arrestors? That could harbor a place for SRB (sulfate reducing bacteria). https://terrylove.com/forums/index....the-rough-in-valve-in-bathroom-remodel.78155/
 

Bigealta

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When i do the peroxide clean i draw some of it into the Hot water tank by opening up a hot water valve for a few moments. It works for me. And yes most of the sulfur smell comes from the hot side. A Tank flush may also help if you have sediment in bottom. Adding a simple taste/odor filter might help extend times between cleaning/flushing pipes and tank. It also adds a very easy way to add peroxide or any other fluid to your pipes to clean them.
 

Mr tee

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If it is just the lavatories and the faucets are connected with plastic or braided stainless steel (over plastic) flex connectors they could be the problem.
 

Bigealta

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you can also try increasing water temp in the hot water tank to kill the sulfur bacteria if this is determined to be where the smell is emanating from.
 

Granger

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Here’s a follow up. I changed the anode rod (which was almost 75% gone) and flushed the tank. Also turned off the recirc pump for a few days prior to the rod change and the smell was still there. I have no idea what to do next.

The three sinks where the smell is coming from are the top floor of our house and they may share the same air vent. The sinks all drain without a problem. The p traps on these 3 sinks are really small diameter pvc. Could it be that when we turn on the water the p trap water level lowers enough to release the rotten egg gas for a few seconds? I’m out of ideas.


Thanks for your help!
 

Joshuasamuel

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Hi,
If it is proven that the sulfur bacteria are the source of the stench, you can also try raising the water temperature in the hot water tank to destroy them. Thanks
 

Reach4

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Here’s a follow up. I changed the anode rod (which was almost 75% gone) and flushed the tank.
A new anode rod, especially a magnesium rod, can increase H2S. For H2S generation reduction, some remove the anode, and put in a brass plug instead. But that does not protect the WH. A powered anode can protect without helping to generate H2S. My favorite powered anode is no longer being sold; I liked it because of the longer electrode.

Yes, running the WH temperature above 140 can reduce generation of H2S by making it uncomfortable for the SRB. When cranking up the WH, you should be using a thermal mixing valve to make the hot water safe at sinks and showers and tubs.

Effective sanitizing the well and plumbing will help for a while for sure. The help duration while can vary a lot. I would hope for many months, but it varies. A better procedure can help increase the duration. Some just pour bleach down the well, and run water until chlorine is detected at each faucet. My suggestion is a more rigorous method.
 

Tuttles Revenge

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The reason the smell is coming from the cold may be the style of recirc being used where the hot water is pumped to the crossover and into the cold water piping. The hot water tank is still the likely source of the problem.
 

Granger

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OK 2nd update. Think I was chasing a red herring. Since I flushed the heater and changed the anode thinking that would fix it and it didn’t, I did an experiment where I closed the drain in the sink and ran the cold water. No smell! When I opened the drain back up I got the smell. So the smell is now definitely coming from the drain pipe. Sorry for the plot twist.

Is the P trap not large enough and the running water breaks the water trap allowing sewer gas to escape? Is there a reason that it only happens on the upstairs sinks? There is no smell until water is running. And only the sinks on the top floor master and casita which I believe share the same air vent. First shot has no air vent I can see. 2nd shot has a really small pvc line which I believe is an air vent?

Thanks for your help and patience
 

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WorthFlorida

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What is the wye connected to? That is not a legal trap in my book. Trap pipe diameter has nothing to do with it your odor problem.
 

Tuttles Revenge

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What is the wye connected to? That is not a legal trap in my book. Trap pipe diameter has nothing to do with it your odor problem.
The PVC is likely connected to a condensate. Pretty common in AC areas. Good chance its got sludge build up and could be a source of smells. Sink overflows too can get smelly.
 
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