Things You'll Need
Slip joint pliers
Penetrating oil, if necessary
Phillips screwdriver, if necessary
Vise grip pliers, if necessary
Water shut-off valves tend to accumulate mineral residue and freeze. Of course, you won't find out until you need to shut off the valve to make a repair on a pipe line, sink or bathtub. Not knowing how to free stuck plumbing valves, though, can lead to broken valves, pipes and fixtures, leading to more expensive repairs. Following a few steps, however, you may be able to get the stuck valve back in working order and finish your plumbing repair job.
Turn off the main water supply valve. This will prevent water from coming out of the stuck shut-off valve once you get it to move. The main valve connects your water utility service line with the water system in your home and could be located inside or outside your home by the sidewalk.
Hold the stuck valve's body with a pipe wrench to keep it from moving.
Locate the valve's packing nut. This is the nut right underneath the handle you grab to turn the valve on and off. If your valve has a visible stem between the handle and the valve's body, this nut will be at the base of the stem, right on top of the valve's body.
Turn the packing nut counterclockwise to loosen the nut using a wrench as you hold the valve's body with the pipe wrench.
Try turning the shut-off valve on and off by hand now. If the valve refuses to move, tap lightly on the valve's body with a wrench to break the stem free of the buildup. Now, try turning the handle with a pair of slip joint pliers, but do not apply too much force. If that does not free the valve, go on to the next step.
Apply penetrating oil to the valve stem, right underneath the packing nut, so the oil reaches around the stem and into the inside threads. If necessary, remove the valve's handle with a Phillips screwdriver to gain access to the stem. Wait for 10 minutes for the lubricating oil to work. Repeat Step 5.
Lock a pair of vise grip pliers on the stem, if it is accessible, and use the pliers to turn the stem counterclockwise about half a turn. Once the stem is loose, tighten the packing nut, replace the handle knob, if necessary, and turn the main water supply valve back on.
Open the shut-off valve completely and then rotate the valve half a turn in the opposite direction. This will make it less likely for the valve to become stuck again.