Absence of a cap is a main reason for water entering a flue. A proper-sized chimney cap should be installed by a chimney professional.
Cracks in the crown - The crown should be sealed or replaced to prevent water leakage.
Deteriorated masonry - Gaps or cracks in the masonry or mortar may cause water to enter the flue. Masonry repairs or a vapor permeable brick sealant can be partial remedies to water leakage problems.
Deteriorated flashing - Flashing should be repaired or replaced in this instance.
Water entry into a chimney is water entry into a home. As with other parts of the home, this fluid can cause damage and encourage mold growth. Trust your chimney’s watertight integrity to Full Service Chimney, thereby insuring years of worry free use.