I’m experiencing an intermittent issue with the sewer gases (rotten onion smell) entering the flat through the bathroom. Very annoying as you can imagine. Bizarrely it “only” happens 2-3 times a week, usually between 6pm and 8pm and it lasts for about 0.5-1h but it then goes away. It seems to happen more frequently in cold weather conditions… but there are exceptions to that.
Some extra detail: We’re on a top floor of a four storey refurbished office building. The neighbours directly below us are not affected by the issue but people opposite sometimes are too. It only ever starts in the bathroom and comes from behind the wall where the vent pipe is. The plumber sent by the developer came earlier this year, did the smoke tests and checked the installation in our flat. Apparently it’s all fine and the issue must be outside our flat. He mentioned that we share the soil vent pipe with the flat directly below so he went downstairs and “sealed” something in the shaft holding the vent pipe (apologies for the lack of technical know-how and wrong terminology). Then it was fine for four months (summer) and it’s just started again!
I’ve done some research and due to the intermittent nature of the problem it shouldn’t be related to the toilet wax seal or t-trap or air admittance valve for that matter (don’t have any in my flat). I might be wrong though so I don’t want to exclude that just yet. It’s definitely not cooking smells either. No smell on the corridors or in the basement.
The plumbers seem to be out of options (!?) but the issue persists so we need to find the solution. Has anyone come across anything similar and managed to fix it? Could this be related to the usage of appliances/water/waste during the peak times?
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