Hi all.
Sewer smell comes from kitchen exhauster(aspirator), it is connected to the chimney. I also noticed when I run wash machine detergent smell comes from the kitchen exhauster, which is again same place. This is a duplex top floor(penthouse) and there is no other place in the flat which has smell problem. Only the kitchen exhauster. Kitchen is on the 1st floor, also a washing machine and a toilet. And on the 2nd floor there is another toilet and bath etc using same main drain pipe. Uses city sewer.

Are you located in the US? The term kitchen exhauster (aspirator) is not one with which I am familiar. I assume that it is a kitchen exhaust fan and should be vented to the exterior. It certainly cannot be vented into a chimney if the chimney is still in use.

Are you saying or implying that the sewer system is or could also be vented through this same chimney?

Hi hkstroud,
Many thanks for your reply.
I'm not located in the US, writing from Europe :) Yes that's a kitchen exhaust fan, seems to me connected to the chimney or maybe exterior(I don't know what is it exactly), chimney is not in use at all. Eventually it is connected to the wall.. My suspicion is that sewer system maybe vented through this chimney or whatever it is.

Well frankly I don't know what to say. Venting an exhaust fan into a chimney is not a good idea. I can see where someone might think so but if you think about it that chimney is full of ash and soot. That has to find its way back into the house.

If someone vented a sewer system in the same chimney that is terrible. All the gasses out of the sewer would be coming up through the chimney. Naturally it is going to find its way back through the exhaust fan. An old chimney would surely have leaks. I can see if someone ran a sewer vent pipe down the chimney but I don't know how you would support it inside the chimney. But to vent the sewer directly into the chimney is just a bad, bad idea.
Be best to knock the chimney down and use the space to run a vent pipe.
Don't know what you could do right now other than keep the exhaust fan running or make some kind of cover for it.

Harold nailed it! Sounds like you have a crossconnection between the kitchen exhaust and your sewer system, As Harold advised, I would seal off 56the exhaust opening until I got some one in to check it out and make it right, Good luck, Tom