It's been a while that I have noticed a faint but terrible smell of rotten broccoli/cabbage in my upstairs. It seems to be coming from the upstairs where the water heater is located. The bathroom is on one side and my bedroom is across and my daughter's room is next to mine. Some days it's stronger than other days. Luckily, I work outside of the home and am gone for over 8 hours a day. I'm not sure what to do? I own my own home. It is a townhouse.