My house smells like sewer. It is only 13 years old. The smell comes and goes, usaully when it is ver cold outside, or very warm outside. It disipates at night and reappears in the morning when the first toilet gets flushed. Please help I

Sounds like your vent pipe is partially blocked. Sewer gas could drift down from your roof line and be pulled into the house but that usually does not happen in both hot and cold weather. I would rod out the vent. Depends on your home and the current weather but this fequently is done from the roof.