How long after root canal should pain continue?

Few days....: There generally is pain after the local anesthetic wears off; the dentist should explain and warn about that depending how invasive the procedure is, whether he had to clear out infection, or abscess at the root. He should also give you a script for pain medication appropriate to the procedure, and appropriate to his knowledge of your pain threshold and ability to handle pain. Call, get advice.

A few days: Sometimes there can still be some pain after root canal treatment, though it should be significantly dimenished from your pre-treatment pain. It may last a few days or even weeks, but should be improving daily. If it persists, be sure to call your treating dentist or endodontist.