If you have a combination bathtub and shower, the piece that enables the bathtub spout and shower head to coexist peacefully is the shower faucet diverter. Just as its name suggests, this mechanism is a small metal rod fitted inside your bathtub spout that can be manipulated to block the flow of water to the main faucet (the bathtub), and divert the water so that it comes out of the showerhead instead.
While there are a few different reasons one of these diverters can get stuck or fail, testing to see if you have a stuck shower faucet diverter couldn't be simpler. In fact, you'll probably discover this without even intending to, as when you turn on your water and attempt to start the shower, little to no water will actually leave the showerhead with a majority of the flow remaining tied to the bath spout.
Fortunately, the solution to this issue is simple. Even if you wind up needing a replacement diverter, an affordable trip to the hardware store and a half-hour of work is the most you'll have to invest in this job. That, and potentially delaying your daily shower, of course.
One of the two primary causes of stuck shower diverters is a blockage.
The diverter is not a complicated piece of technology. It physically moves from one position to another to create a physical barrier for water. So, if buildup and blockages have formed that restrict or block the movement of the diverter, it's crippled.
The quickest fix for a blocked faucet diverter is to just give the handle a gentle, well-placed tap. Your diverter's handle may be a lever that you can flip like a light switch or a vertically oriented stem that you can pull up or push in. Either way, the handle is directly connected to the inner diverter. Jostling or tapping the handle in just the right way may be all that's necessary to shake a blockage loose.
Make sure you're being gentle. You don't want to damage anything worse than it may already be damaged. If this doesn't work, it doesn't mean that you're not tapping or jostling hard enough. It means that the problem is something deeper than a simple blockage, and you'll need to try a different approach.
There are two areas in your bathtub spout that can corrode and impact the diverter's function. The threads on the screw that connects the pipe to the spout can corrode or crack, and the spout's finish can corrode, flake off, and cause blockages. In severe cases, if such damage is left untreated and you continually attempt to use your shower or tub, water can trickle along the pipe and saturate the inside of the wall.
Depending on what kind of faucet you have, there are two distinct ways to see if any cracking or flaking is causing blockages.
Pull Up Faucet
Gently work the handle with the pliers, pulling it out a little at a time. Once you have retrieved it, clean it thoroughly and then place it back carefully.
Look for the screw under the faucet spout and unscrew it, enabling you to turn the faucet upside down. Use a pair of needle-nose pliers to pry the black rubber washer loose. Check for any debris and remove it as necessary.
Replacement Shower Faucet Diverter
If the shower faucet diverter is stuck because the washers are old and have broken or the plastic valve diverter inside the pipe has broken, then it is time to replace the faucet itself. The diverter is not an overly expensive mechanism to buy and replacing it may be easier than attempting to fix it.