Bathtub spouts can go bad in three ways: First, the diverter can wear out so it no longer blocks the water flow and sends water to the shower head. Second, the threads inside the spout can crack or corrode where the spout screws onto the pipe. Water can then trickle along the pipe and drip inside the wall. Finally, the spout's finish can flake off or corrode.
Replacement is the solution to any of these problems. A new spout ($10 to $20) and everything else you might need are available at hardware stores and home centers. But before you buy a new spout, determine what type you need. First look under the spout. If you see a setscrew (Photo A), you have a “slip-on” spout.
The setscrew might be smaller and harder to see than the one shown here; you may need a flashlight to spot it. Replacing a slip-on spout is easy: Just loosen the setscrew (usually with a hex wrench) and pull the spout off the copper pipe that protrudes from the wall. Twist the spout as you pull and be gentle so you don’t loosen any pipe connections inside the wall. Then slide on the new spout and tighten the setscrew.
If the spout doesn't have a setscrew, it's a screw-on spout (Photos B and C). Twist the old spout counterclockwise to remove it. If the pipe that protrudes from the wall is copper with a threaded fitting (Photo B), simply cut off the fitting with a tubing cutter ($10) and install a new slip-on spout (Photo A). If the pipe coming out of the wall is steel (Photo C), you need a new screw-on spout.
Ideally, the new spout will fit perfectly onto the old pipe. But there's a good chance that the pipe protrudes too far or not far enough. There's also a chance that the threads are too corroded for you to screw on a new spout. Either way, you'll have to remove the old pipe (Photo 1) and screw in a new pipe of the correct length (Photo 2). Short sections of threaded pipe (called “nipples”) are usually available in 1-in. increments. They cost less than $2 each, so buy a couple of different lengths and save yourself a trip back to the store.
These are the three most common types of spouts.
Plumbers tell us that leg-shaving is the leading cause of tub spout trouble. The spout makes a convenient footrest for shaving, but that can damage the diverter or loosen pipe connections.