Do angle stops fail?

Do angle stops fail, yes, angle stops, also called angle stop valves or fixture shutoff valves located under sinks and behind toilets, can and do fail, especially older types and those that have not been operated for years. Common failure modes include valve will not fully shut off water when closed, allowing trickle or full flow to continue, due to worn washer, damaged seat, or mineral buildup preventing tight seal. Valve leaks at stem or packing, dripping water around handle, due to worn packing or O ring. Valve handle breaks or becomes very hard to turn, or spins without stopping flow, indicating stripped stem or detached gate in old gate style stops. Visible corrosion, rust, or calcium buildup indicates deterioration. Old multi turn gate style angle stops with round or oval handle that require multiple turns are especially prone to failure after 10 to 15 years, while modern quarter turn ball type angle stops are more reliable and last 15 to 25 years but can still fail if low quality or exposed to hard water. Factors that cause failure include hard water mineral deposits, never exercising valve, over tightening, and cheap materials. To prevent failure, exercise angle stops annually by turning off and on, and proactively replace old gate style stops with quarter turn ball type during remodels, as failure during leak emergency can cause significant water damage.