I heard a loud pop so quit. The unit is working well. Should I be worried?

Need more info. Tell us what u did and what happened.

Chuck

If the boiler is not leaking, you are most likely okay. Now, if the boiler is cast iron, and you flushed it with cold water when the water in the boiler was hot(like 180 degrees), you may have cracked the heat exchanger, but if you did, you would see water leaking onto the floor. If no water leaking, like I said, you are probably all right. Always shut the boiler off and allow it to cool to room temp before adding cold water or flushing with cold water. Cold water shock to a hot boiler can crack the boiler heat exchanger.