Hi all,
The vent cleaners were here yesterday and solved the issue. It turned out that the connection between the duct inside the house and the part outside in the water heater shack (that housed the part that the plumber replaced) was bad. It wasn't connected fully. Vent cleaner said that the plumber didn't check it properly after he replaced the part. So, the hot air and moisture was blowing into the walls and causing the smell.

I'm uploading the photo to show you that part. Vent cleaner says to put expanding foam around the duct, which I'll do over the weekend.

Plumber charge: $3000
Vent cleaner: $140 (and basically redid some of the work plumber did)

Thanks again for all your advice! This is a great forum.

Hey, thanks for the update. And kudos to the cleaners. And shame shame shame shame on the plumber (I wouldn't have the guts to call them a plumber, but that's just me, he he).

3000 bucks, for what? I hate to say it, but you got ripped.
At the very least, I would never call that plumbing company again.

I'm sure I did. It started as less than half of that amount but after the gas pipe replacement and dryer/water heater duct replacement work, it ballooned into that much money. Didn't help that these guys calculate labor in a rather unethical way. I (nor any of my family or friends) will not be giving them any business ever again, that's for sure!

Thanks for telling us the end of the story. I'm very sorry but unless the plumber ran you a new gas line, you got cheated and cheated big time. The duct repair was handyman work and apparently he can't do that properly.

Sorry we couldn't find it.

Finding a good, honest, tradesman can be difficult. They are out there, in fact most are. You just have to find them. I wish there was some reliable method but I don't think there is one. To say get 3 estimates is a great lip service but for these kinds of things is often not practical. Word of mouth is the best reference. My suggestion would be to find a good handyman and keep him close. If necessary pay him to be your consultant.

I would have never touched your gas line but would have probably suggested some one.

Find him now buy asking around, before you need him.

Thank you. Ironically, I was referred to this family-run plumbing company (who's been in business for 40+ years) by a handyman, who in turn was referred to me by a family friend. I was excited to get a handyman referral, so I was thinking about employing him for various fixes around the house but with this plumber experience, I'm now on the fence...

Anyway, thanks again to all and please keep the advice coming, for those of us who are not in the business and really need expert advice!