Identify Failure Point (Brittle Washer)

What happens here

Once the valve stem assembly is completely removed, carefully examine the black rubber washer located at the very end of the stem. This is the critical component that often fails. The video demonstrates that this washer typically becomes brittle and hard over time, eventually cracking or breaking apart. Test its flexibility; if it's stiff, cracked, or falling apart, this is the primary cause of the valve's malfunction. The presenter emphasizes that fragments of this deteriorated rubber washer can dislodge and travel into your household plumbing, potentially clogging faucets, dishwashers, or toilet fill valves, leading to significant plumbing headaches.

Goal: Understand and visually confirm the primary cause of multi-turn valve failure.