another sewer gas mystery

In my last house, I experienced an occasional but obvious sewer gas smell from at least two of our three toilets. The third one got little use. I did many things to troubleshoot. The smell was definitely coming from inside the bowl.

Both offending toilets had overflowed at one time or another, so I figured dirty water had risen above the fill holes and leaked into the upper rim, leaving deposits on surfaces that never get flushed. I finally ended up taking one of the bowls outside for a thorough cleaning. Among other things, I turned it upside down and filled interior of rim with bleach. After carefully reinstalling the toilet with a new ring, the smell eventually returned. Mystery was never solved.

Shift forward in time. I recently moved into a two-year old house with two toilets. One had a defect and had to be replaced. Since then, I'm certain this one has never overflowed. To my surprise, I've had several instances of a definite sewer gas smell from both toilets. I'm sure it's coming from the bowl because the smell hits you in the face when you open the lid. I'd guess this has happened about four times in as many months. No amount of bowl cleaning eliminates the odor, but the ordor seems to go away as suddenly as it began.

This makes no sense to me. The inside of the upper rim is the only part of the toilet I can't clean, at least not directly. But since the toilet bowl is new and never experienced an overflow, the rim would only have seen clean water! So where is the odor coming from?! I always thought a toilet trap provides absolute protection from sewer gases.

Or is this simply an unavoidable fact of life?

#1 Do you have well water?

Is there gurgling or bubbles coming back up at any time or in any of the other fixtures, (could a vent be plugged), bird nest or some thing, or some other type of blockage.

HandyAndy said:

Is there gurgling or bubbles coming back up at any time or in any of the other fixtures, (could a vent be plugged), bird nest or some thing, or some other type of blockage.

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I haven't noticed this. In any case, if a vent were obstructed, it is my understanding that would interfere with flushing or slow down sink drains. Haven't seen this at all. Also, I've only noticed the odor a few times over a period of several months. Of course, I don't make a habit of sticking my head in the bowl It may be just a matter of degree...?

To answer previous poster...
We're on municipal water (and sewer).

David

If your municipal water is drawn from wells, as is common, you may still have an issue with water odor.

uniberp said:

If your municipal water is drawn from wells, as is common, you may still have an issue with water odor.

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Yes, our municipal water comes from wells. It has a very slight odor. However, the only mineral it contains in abundance is calcium.

The sewer gas smell is unmistakeable. No possiblity I'm smelling the water!

If the wax seal is compromised, it won't necessarily leak water all over things - it would only leak if there was a clog and the water backed up.

Do the toilets move at all, even the slightest? If so, then the wax seal could be compromised. It can easily leak gasses and not leak moisture.

jadnashua said:

If the wax seal is compromised, it won't necessarily leak water all over things - it would only leak if there was a clog and the water backed up.

Do the toilets move at all, even the slightest? If so, then the wax seal could be compromised. It can easily leak gasses and not leak moisture.

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When I replaced the one toilet a few months ago, I was very careful with the ring. I haven't checked the second toilet. Perhaps I should. In any case, they are rigid on the tile floor. Having said that, when the odor has occured, it usually waffs up when I open the seat, as if it were accumulating inside the bowl.

Just because a toilet doesn't rock, doesn't mean the seal is good. Are the flanges sitting on the finished floor? If not, you have a problem.