Why is my fireplace flashing and how can I fix it?

A flashing fireplace could be caused by a buildup of soot or debris in the chimney, a faulty gas valve, or a problem with the ignition system. To fix it, you should first check for any blockages in the chimney and clean it if necessary. If that doesn't solve the issue, you may need to have a professional inspect and repair the gas valve or ignition system.