What is causing an unknown smell in my house?

Try closing all the internal doors and see if you can pinpoint which room it's coming from.

Then check:

1. Is there a gas leak?

2. Has any shopping been left in a bag anywhere?

3. Empty all the bins!

4. Is it mushroomy? Check all wood for rot.

5. Shift all the furniture and clean under and behind things. Watch out for dead mice.

6. Is it the dog?