When I put on the bathroom fan I smell a sewage odour escaping from the heating vents?? Yes definitely from there, not from the drains. I am on septic, and have recently replaced the old copper piping due to corrosion & replaced with PVC piping. I cannot figure out for the life of me why the smell would be coming from the heating vent!

You exhaust fan is creating a slight vacuum in the room and pulls the sewer gas from a bad trap or seal. A bad toilet wax ring is usually the biggest cause. Did you replace and of your drains with PVC? Did you work on the vent stack at all?

Good thinking Ballengerb1. Sorry, system doesn't allow me to leave you positive feedback...

For the poster: when you replaced sewer line: did you hook up all vents to it ?

And do you know if you are using a AAV ( air admittance valve) anywhere in this room instead of a vent