A leak at the stem under the handle is often worn packing, and some valves allow a small packing-nut adjustment. A leak from the valve body, or a valve that no longer shuts, is replaced. Replacement needs the water isolated upstream, which in a commercial building can mean shutting down a whole zone.
Where is the valve leaking?
| Leak location | Usual meaning | Usual fix |
|---|---|---|
| Under the handle, around the stem | Worn or loose stem packing | Small packing-nut adjustment if the maker allows it, otherwise replace |
| From the valve body or its seam | Failed body or seal | Replace the valve |
| At a threaded or soldered joint | Joint problem, not the valve | Remake the joint |
| Drips from the outlet when closed | Valve no longer seals | Replace the valve |
NIBCO's instructions for its bronze ball valves say that when stem leakage occurs, tighten the packing nut under the handle in 1/8- to 1/4-turn increments, just enough to stop the leak, and not past the torque the maker specifies. The same document says there are no field repairable or replaceable components within the pressure vessel of that two-piece ball valve, and that it should not be disassembled for internal repairs. So a body leak is a replacement, not a rebuild.
Why do old valves fail?
Valves that sit open for years seize or stop sealing. NIBCO recommends exercising valves from fully open to fully closed periodically, such as at least once every 6 months. Many buildings never do, which is why the valve that has to work during an emergency is often the one that fails. Ball versus gate valves behave differently as they age.
What does replacement involve?
The valve can't be swapped under pressure. The plumber needs the water off upstream, which may be the next valve back, a riser valve or the main. Phoenix Water Services advises that you not use the meter valve for this, since that takes a special tool and you may be held responsible for damage to the meter. If the upstream valve also leaks or won't close, the shutdown grows.
That is why a weeping valve is worth fixing on a calm weekday. A planned shutoff lets you notify tenants and schedule after hours, and testing the main valve tells you whether it will hold. For a small fixture stop, see the handle-leak page.