For about the last year, we've been wrestling with a horrible sewer odor downstairs that comes and goes. It seems to come from the crawlspace access, yet I've had a plumber and another technician go down there and not see anything out of the ordinary. The smell can be like a musty wet mildew smell or like the subject tag says "sewer". We do have a HE washer, but we've cleaned this with cleaning tabs bought at the Home Depot recently. The smell will change with the weather as well. Whenever there is a change from hot to cold or vice versa, it gets worse.

Bob

Calling a tech means possibly you called the wrong type?

Did you find the "technician" under T in the yellow pages?

If people were honest they would advertise i n the pages under T for tech and then sub listing such as X ray TECH and Dental TECH and electronics tech as plumbing requires a license thus you need either a journeyman's card or Masters license.

Not everyone who calls themselves a "plumber" is actually licensed and many low life employers trying to beat the licensing laws say "we are sending out a tech" as they cannot legally say we are sending out a plumber.

If the smells change with the weather possibly it has to do with something called heat goes to the absence of heat AKA heat goes to cold so if the house is cooler then the outside ambient temperature the down draft from the vent terminal can cause a trap seal loss same with evaporation and negative and positive pressures especially if the Fresh air inlet and vent terminal are blocked.
Never call a TECH do to electrical /plumbing or HVAC as you may hire the wrong tech fro the task at hand UNLESS the tech has various formal training in all aspects of every trade