It does suck big time. My thoughts too but water is coming from same way as It's always been and I do believe it's same pipe delivering water to my house too so...I thought air too and asked million questions if he cleaned with something or put anything in there but no.
Well I've asked that question too mate but she seems more upset than him that they are dying. Honestly never seen anything like it.
We've checked that too Flip. I thought maybe some of the air from the gas vent was coming back into the attic. But again his gas safety inspection was about a month ago ( a month after it started) and he specifically asked the guy to check the out vent readings as he thought it smells funny in their bedroom. Inspector said all readings are absolutely in range..
I don't know what to think. Will keep you posted if that mistery unfolds.