Sometimes, you realize that one of your major characters is supiciously lacking in flaws. She is usually a person like yourself, but she is lacking in defects as well as in color and definition. When this happens in a piece of fiction you're writing, it is a sign that you are identifying too closely with her. Just as you try to show your good and hide your bad, you are protecting a fictional person.
If you're identifying too closely with your character, look around, see if you can find someone else who could embody your character. She'll begin to exhibit all kinds of personality traits.
Another way to break the spell of the flawless character is to elicit the opinion of another character in the novel or story, one who dislikes, resents, or holds a grudge against the paragon of virtue.
A character without flaws has nowhere to go. He can't change or grow.
When writing, the flaws that interest you are not the ones you assign, but those that emerge in the course of the story.
People, fictional and real, are not perfect, like fresh-from-the-factory tables. They come with their faults built in, mingled and confused with their virtues. Whenever you find you're dealing with a character without flaws, take it as a sign that you have not done your work. You have not imagined your character fully, have not considered her through the eyes of the other characters. Finally, you have not cut the umbilical cord. You are protecting her, shielding her, and, at the same time, imprisoning her in her own virtue. It is time to let her go so she can fail and change and grow.