sewer gas smell from new shower drain

Ever since the p-trap was replaced in our shower drain about two years ago, we get an occasional sewer gas smell. We get the smell every few weeks. A mix of boiling water and vinegar takes care of it, but it would be nice to solve the problem once and for all. The shower is used regularly and there is always water in the p-trap. The house is 60-years-old and on a concrete slab. Any thoughts?

Thanks, Tim

There seems that some information is missing. The trap only was replaced?, why? how was this done in a concrete slab? need more info.

1 of 4 things are happening.

1. There is a leak in the trap and the water is slowly draining out of the trap.
2. You have improper venting and the trap is being siphoned dry.
3. The trap arm for the shower is an S-trap and the trap is being siphoned dry that way.
4. You have an overly warm bathroom and the trap's seal is evaporating away fairly quickly....

Those would be my guesses.

You could also have a long drop pipe to the trap and it is getting "fouled" creating the odor. The drain cleaner periodically would "boil" it out until the "stuff" came back.

Shacko -- The house sits on a slab. The drain is in the slab. The drain started to drain slowly and then eventually backed up. It turned out the original p-trap had corroded away. So, we had it replaced. I'm a novice here. Is there anything else you would need to know that could be helpful.

Doherty -- Under all four of your guesses, the trap would go dry at some point, correct? I've been watching it long enough that I'm pretty confident in saying it never goes dry.

HJ -- It's about 12 inches down the drop pipe to the top of the water. Is that long?

Thanks for all the replies. I sure appreciate it.

If the trap corroded out it indicates that the piping system under the slab is probably galve. there's a chance that part of that pipe has a hole in it causing the smell, my best guess.

Twelve inches of unprotected riser from the trap could grow all sorts of crud. The trap prevents anything beyond it from impacting the dwelling, but can't do anything before it. No, it's not too long, but it might be nice if it were shorter. Is this drop straight down to the trap? If not, then it's even worse.

Thanks gentleman.

I'm hoping it's just the long drop pipe.

Nope the trap doesn't have to drain completely. It just needs to drop below the trap seal point. There could be a leak just below the trap seal elevation *shrugs*