Fixing a Leaking Water Supply Valve

Why Supply Valves Leak

The shut-off valves under sinks, toilets, and behind appliances are designed to control water flow for maintenance. Ironically, because they are rarely used, they develop leaks when you finally need them. The rubber washers and packing material dry out, corrode, or become coated with mineral deposits. Gate valves are especially prone to failure because the internal gate mechanism corrodes in the open position over years of disuse.

Tightening the Packing Nut

Many valve leaks can be fixed by simply tightening the packing nut — the hexagonal nut directly behind the handle. Use an adjustable wrench to tighten it a quarter turn clockwise. Turn the handle back and forth a few times, then check for leaks. If the leak stops, you are done. If tightening the nut makes the handle too difficult to turn, the packing material needs replacement rather than compression.

Replacing the Packing

To replace valve packing, turn off the water at the main shut-off valve. Remove the handle and unscrew the packing nut completely. Pull out the old packing material — it may be a rubber washer, graphite string, or Teflon packing. Replace it with the appropriate new packing material. Wind graphite packing string clockwise around the valve stem (three to four wraps), or install a new rubber packing washer. Reassemble and tighten the packing nut until the handle turns with moderate resistance.

When to Replace the Valve

If a valve is severely corroded, cracked, or will not turn at all, replace it entirely. For soldered connections, this requires sweating the old valve off and soldering a new one. For compression or threaded connections, disconnect and replace. Consider upgrading to a quarter-turn ball valve — these are more reliable, easier to operate, and less prone to seizing than multi-turn gate or globe valves. If working with copper pipes, push-fit valves eliminate the need for soldering.