The chimney crown is a very important part of the chimney system in your home. Its function is to repel water and protect the bricks below them. Once water is allowed to leak into the mortar, bricks will become loose and the integrity of the chimney can be at risk. Making sure the crown of your chimney is in good working order and built correctly is extremely important to the health and maintenance of the structure.
This is why the crown is one of the many areas that are inspected each year when a certified chimney inspector comes out to do the inspection. There are times when home owners have a home inspector or roofer come out and take a look at their chimney system and things get missed. This is because those specialties are not in the areas of chimneys. On many occasions there is thought to be a roof leak and it turns out to be a chimney leak due to the crown eroding or damage or to mortar erosion that is missed along the crown. If left alone for long periods of time these small issues can become large ones and cause chimneys to collapse. Once this happens the only solutions are to either wall up the fireplace and roof over the chimney or rebuild the chimney.
Sometimes the crowns are damaged due to bad construction. Not all stone masons know how to build good chimney systems. If not built correctly in the first place, chimneys can be a dangerous appliance in your home releasing toxins and gas into the air instead of up the chimney. There are too many things that need to be taken into consideration when building a chimney not to hire an expert in the field.
One way you will know the chimney company you hire is checking everything they need to is them getting up on your roof and doing a physical inspection of the cap and crown. Mortar joints can be seen from the inside by a camera they run up the chimney walls and on the outside by the same physical inspection. This is the only way this part of the chimney can be properly inspected.