Manufactured fireplaces often have refractory panels(concrete like) panels that are installed inside the firebox of the fireplace. Refractory panels will limit the heat transfer into the metal sides of the firebox. Large cracks (generally those over ¼”) can cause excessive heat to transfer to the metal shell of the fireplace. This can eventually cause the metal to deteriorate and those cracks in excess of ¼” should be repaired.
Hairline cracks can appear due to the heating up of the panel causing it to expand and when the refractory panel cools, it contracts and eventually will crack. Cracks can also be caused by excessive heat from an improper burn in the firebox i.e. large volumes of paper or using flammable liquid to light fires.
Panels are also cracked when moving adding or moving large logs in the fireplace. Care should be taken to assure that the logs are not thrown against the panels. Thermal shock from through water on the fire can also cause refractory panels to crack. Proper curing of replacement panels is critical to assure that the panel will last a long time.
One can analyze a crack to determine the seriousness by checking the fireplace manual for guidelines regarding nature of the cracks. Using a dime or something of similar thickness, if it can be inserted into the crack consideration should be given to replacing the brick panel. If the brick panel has wide or multiple cracks, it would be wise to replace the brick panel with new panels that are easy to install.
Some cracks can be repaired with castable refractory cement which is easily applied to the crack. That however may not give you the desired appearance. Manufactured replacement panels, available in either vermiculite or brick are the best choice. Vermiculite panelsare very easy to cut whereas the refractory type panels require a saw with a masonry blade.
