Your chimney is unlined

Your existing lining is cracked or broken

When flue tiles are cracked, smoke and heat can leak out of the flue system. After removing these cracked tiles for a chimney reline heavy smoke stains could be seen in the chimney interior behind where the tiles used to be located.

Your chimney is unlined

Your existing lining is cracked or broken

This is similar to a smoke stain on the outside of a chimney were a smoke leak occurred.