The answer to 'why is my roof vent water stains' is that roof vents are a common source of water leaks and stains. This is usually caused by issues with the flashing, sealant, or ventilation pipe around the vent. Over time, these components can crack, deteriorate, or become damaged, allowing water to seep in and create stains on the ceiling or roof.
Some common signs of a leaky roof vent include water stains, mold growth, or dripping water around the vent. If left unaddressed, a leaky vent can lead to more serious roof damage and interior water damage. In many cases, repairing a leaky roof vent is a job best left to a professional roofer, as it may require replacing the flashing or sealant, or even the entire vent unit.