Here are several factors that may cause search coil failures:

1. Physical Damage: One of the most common causes of search coil failure is physical damage. Dropping the metal detector or hitting the coil against hard objects can result in cracks, breaks, or other forms of damage to the coil, leading to malfunction.

2. Water Damage: If the search coil is not properly waterproofed or if it is submerged in water beyond its waterproof rating, water ingress can occur, leading to internal damage to the coil's components.

3. Interference: Interference from external sources such as power lines, other metal detectors, or electromagnetic fields can disrupt the proper functioning of the search coil, leading to inaccurate readings or complete failure.

4. Normal Wear and Tear: Over time, normal wear and tear can degrade the performance of the search coil. Continuous use, especially in rough terrain or harsh conditions, can gradually degrade its sensitivity and accuracy.

It's essential to handle and maintain the metal detector properly, following the manufacturer's guidelines for usage, storage, and maintenance, to minimize the risk of search coil failure. Regular inspection and prompt repairs can also help identify and address potential issues before they lead to complete failure.