Sewer gas smell coming from wall under vanity?

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Hi all, hoping someone can help me. I'm handy but usually leave plumbing to someone who knows better than me what they are doing (more of a carpentry girl myself, though I fixed all the other toilets in the house that just needed new gaskets and valves, etc).

I had someone in to fix one toilet in our new house -- it was loose and needed to be removed and rebolted and the wax ring replaced. Turns out they didn't replace the wax ring (!) so it was damp smelling for several weeks until I made them come back out and when they removed the toilet again, I saw the old degraded wax ring. They replaced it with a new one and I hoped all would be well.

That was about 2 weeks ago. Suddenly tonight, there was a very strong sewer gas smell in that bathroom. I tracked it down not to the toilet, but to the openings in the wall under the vanity where the pipes come out. Flushing every toilet and running every sink in the house didn't help. No clogs that I can detect. For a temporary fix I duct taped around the holes in the wall because it was SO stinky. That worked, but of course it is a bandaid and not a fix.

What do you all think is the cause here? My understanding is that a wax ring or seal issue with the toilet would make the smell come from over there. The smell is definitely wafting from the inside of the wall where the pipes come through under the vanity, though, which is on the other side of a door about 5 feet from the toilet. Plus, no smell from the plumbing access panel that's behind the shower (on the same wall as the vanity about 3 feet away). I'm stumped (which admittedly isn't hard to do with plumbing).

Just looking for advice to see if I need to yell at this guy to come BACK and fix it again, or if I need to find someone new and sort of either hope they know better what they are doing, or I can point them in the right direction (vent issue? the wax ring? something else? what's likely?).

This is a second-floor bathroom, we're on sewer (not septic) and no other plumbing fixtures in the house have the odor.

Thanks for any advice!

Jeff H Young

In the Trades
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its not automatically the wax ring but it could be. could be its been leaking and there is molds in the wall too , could be the flange was low and the guy that was too dumb to replace the wax ring the first time didn't know it was low so instead of doubling up or installing a thicker wax just used a standard wax. or a crack / break in pipe
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