About 10 years ago, some of our friends cleaned their own chimney in a house they purchased. They thought they had done a good job. But one night the chimney and roof caught on fire, so obviously they hadn't.
My hubby was a chimney sweep at the time, and offered to check their chimney and fireplace, but they refused. Because they did not get an "official" inspection done before hand, their home owners insurance refused to pay for repairs. They were out of their home for a number of months while the house was repaired because they had to pay for it themselves. It was quite an expensive lesson for them.
So if you have never had it officially inspected, I would contact your fire department or a local chimney sweep to have it inspected to make sure it is in good shape.