I would call another plumber. Get a second opinion about the sewer gas. It's coming from someplace and you've got to find it. Do you have an old washing machine hookup that's allowing the gas to enter the home?

Sara:

You have many dynamics here so you need to break them down and eliminate them one by one.

IâÂÂm assuming the vent under the sink is a supply vent (the kind that pushed out cold and hot air). If itâÂÂs an air admittance valve, I have seen those allow sewer gas in when not working properly. An AAV allows air into a drain line where a traditional vent doesnâÂÂt work. These are very common on kitchen islands.

Go to the following site and see how and AAV is installed and then look under your sink to see if you have one. If you do, it may need to be replaced.

http://www.diyadvice.com/diy/plumbing/kitchen/install-air-admittance-valve/

The ERV could be your problem but I doubt it. If the ERV was installed improperly where it creates a negative pressure in your home, it could be drawing in sewer gas. This contradicts how ERVâÂÂs are supposed to work so I doubt this is the issue. You would need a very large ERV to put an entire home under negative pressure.

Sewer gas is in your plumbing drain lines to the point of your sink traps or other fixtures. We have a soaking tub in our master bath that never gets used. Once that trap dries out, I get a pleasant reminder of sewer gas to run the water to refill the trap. That little bit of water in the trap keeps the sewer gas from coming in.

Let us know how it goes and maybe we can give some more feedback.

I suspect mepop is on the right track (and is way more experienced than me).

I was just going to add that if none of that works out, I have found that wastewater sitting in the dishwasher drain line can get funky if it sits several days. Usually I would only smell it when the machine pumps it out for a few seconds before starting the next load. So, after a load runs, I dump out any water caught in the clean dishes, close the door, let it drain into the sump for a couple seconds, then turn on the machine and let it pump for 5 seconds. That seems to get it pumped out.

However I still think you have a sewer gas leak or a clogged vent as mepop suggested.

My first thought was to tell you to check all traps to make sure you have water in all of them. I also think mepop is on the right track, especially with the AAV for the island sink.

Once I had a smell coming from my dishwasher that was driving me nuts. I discovered that when I had replaced my disposal I hadn't secured the discharge hose into a loop as kind of a trap and apparently some gunk from running the disposal was managing to back up into that discharge hose and was causing the funky smell in the dishwasher. It doesn't take much to cause a big stink. Check all your traps, even the dishwasher discharge hose.

I would venture my best guess sewer gases are entering your dwelling. The only thing separating the sewer system from your living space is a few ounces or water in each trap, and a secure vent stack.

Somehow the methane from the sewer is bypassing your traps. I have seen vents that have enough occasional plugging due to a piece of roof shingle down the stack to cause enough back pressure to blow the water seal in the trap, not the same trap everytime.

I don't read where the plumber checked the main and secondary plumbing vent(s). AAV's fail regularly. Change it, they are inexpensive and simply screw on and off. Is it tight?

The big change you have is the ERV system. It is very possible it is bringing gas in with the fresh air somehow.

Mepop said;

The ERV could be your problem but I doubt it. If the ERV was installed improperly where it creates a negative pressure in your home, it could be drawing in sewer gas. This contradicts how ERVâÂÂs are supposed to work so I doubt this is the issue. You would need a very large ERV to put an entire home under negative pressure.

It may not be a negative pressure issue but may be bring in gas with the fresh air.

A new(qualified) plumber is a must to take a look at it. If you smell sewage open the windows, we don't want anyone especially the kids exposed, it can and will make them sick eventually, this are some very bad things in gaseous form here. Don't want to scare anyone but it is explosive if in enough volume. Learn about sewage gases.

Post this over on the plumbing forum and mention it's a cross post. This problem has been discussed before when I was a member over 10 years ago I recall.

Johnny D

Edit, copied from Wikipedia,

Sewer gases may include hydrogen sulfide, ammonia, methane, carbon dioxide, sulfur dioxide, and nitrogen oxides. Improper disposal of petroleum products such as gasoline and mineral spirits contribute to sewer gas hazards. Sewer gases are of concern due to their odor, health effects, and potential for creating fire or explosions.[2]

Lets definitely rule out sewer gases first, then rest assured there is plenty of time to find the source of the odor.

This post was edited by SouthernCanuck on Fri, Nov 15, 13 at 0:38

Wow, I can't thank everyone enough for these thoughtful replies. The crazy thing is that we haven't noticed the smell since I wrote the email! However, it was so strong off and on for several weeks. Any sense of how we could explain that? In the meanwhile, we will follow up on these great suggestions and report back! :-)

Thanks again,

Sara

"I would call another plumber. Get a second opinion about the sewer gas. It's coming from someplace and you've got to find it."

I agree with this.

Do you have a fireplace or use gas appliances? I have heard that crumbling chimneys or cracked vents can allow noxious gas to enter.

A link that might be useful:

www.csia.org/homeownerresources/Gas_Appliances_Your_Masonry_Chimney.aspx

It may have many a reason why the odor is no longer present which is great,from a dry trap in any sink drain or due to a dry drain going from the basement to the city sewer. I didn't mention the basement drain of which I was remiss to do so. These drains are often the culprit as they don't see any fresh water added to them unless there is an overflow onto the floor, a good amount at that.

If anyone has a basement drain to the town sewer systems add water to them a few times a year at least so they don't go dry due to evaporation.

I'm having the same problem as New England Sara right now. I smell is coming out of my kitchen sink. Like Sara, it comes and goes. I checked all the connections under the sink and even went down to the basement to check the sewer line and everything looks good. I suspect a bird built it's nest in the vent which is in the roof above my kitchen. I set up a bird feeding station outside my kitchen window so I can see the birds. Unfortunately, the roof is in the same general area. Only one way to find out.

lovetogarden:

You can't play around with potential sewer gas. The stuff can be deadly. Get a plumber.

Garbage disposals do get smelly form time to time; years ago an apartment manager advised us to try running cold water into our disposal while adding dishwashing liquid detergent (not dishwasher machine soap), then to stop the water and let the disposal suds up a bit...this works really well if the problem is in the disposal unit itself.

Worth a try, as it is very simple to do.

To help clean inside upper rim of garbage disposal use a new toilet bowl brush right size for the opening. Dawn or other dish cleaning soap will work great for this purpose. (Keep toilet brush for this purpose only).

Slimy Crud accumulates under the deflector flap over the opening. Some machines have removable deflectors and others do not.

Ask a drainage company to check that there is a working non return valve in the drain connecting to your house, you could be getting smells coming back to your home because it is damaged, especially if your drains connect to a rising main. Good luck, callout should be free.

My town comes out and checks the line outside so it doesn't cost me. If you are on town water/sewer then it shouldn't cost you anything either since that is built into your sewer/water taxes.

Not a plumber but it seems to me if all your drain traps have water in them, and the vent pipes are unobstructed on their way to the roof, there is no need for a backflow prevention valve on your sewer lateral (pipe from the house to the main). Some people need them especially in places where sewers often back up, it can save you from a sewage flood, but most houses don't have them.

Mine is an old cottage which used to have a septic tank. The new mains on the road is apparently my responsibility and it connects to a rising main. The non return valve is broken and we get awful sewage smells come back up to our garden and occasionally in the house. It's not good for our health. And, it's going to cost over £800 to excavate and repair.

If sewage is getting loose in your garden, it sounds like the valve is not only broken, but the pipe is leaking too.

Edit: I am not sure how it is where you live, but in the US, the local sewer authority is responsible for the main (under the street). The 'lateral' that goes from house to the main is the homeowner's responsibility. And yes they are expensive to dig up and repair.