A chimney can most certainly leak! There are many different places that a chimney can leak from too, so it's not always as simple as just installing a chimney cap. A few other places that a chimney can leak from are: the chimney crown, the chimney flashing, the chimney bricks, and from a defective chimney liner. Any one of these areas can cause what appears to be a severe leak, so attacking all of these areas and making sure that they are all watertight and up to today's codes and standards is really the only way to full stop and prevent a chimney leak.