One can know without being certain. The difference might, at first, just seem to be semantcs; however, there are arguments to how knowledge and certainty are different. One can know, in their own mind that they did something via a series of mental images that they are sure are correct. On the other hand, they no objective proof to verify this knowledge. When asked, "How can you be certain?," it is implied, "What proof can you offer?" Certainty is knowledge which is maximally justified. So, using this argument, one can know that they locked the door, without being certain that they locked the door.
Hope this helps,