That small knob on top of your bathtub faucet is the shower diverter, a device that switches the water flow from your bathtub to shower and vice versa. These knobs can stop working, which can cause the faucet to drip or leak. In other cases, the knob gets stuck and stops rerouting the water and you may not be able to use your tub or shower. When diverters can't be fixed, they need to be replaced.
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Shower Diverter Home Remedies
Before deciding to replace a stuck shower diverter knob, see if you can fix it with some cooking spray. Try to loosen the knob first by pulling it up and down a few times. Spray it several times for lubrication and see if this helps. Clean the faucet and tub area when finished.
Another method is to get a large, durable plastic bag and a large container of white vinegar. Pour the vinegar into the bag and wrap the bag around the spout. Secure it with a rubber band, and leave it sitting for three to four days. Check every few days by removing the bag and trying to use the shower diverter knob again.
Removing the Faucet
When those fixes aren't successful, try replacing the knob itself. These are typically inexpensive and the installation is fairly simple. First, turn off the home's water supply and tightly seal off the tub's drain with duct tape. Gather your tools, including a screwdriver and pipe wrench.
You'll now need to remove the tub's faucet. Look at its underside and see if there's a hole and set screw. Use a screwdriver to remove the screw. Twist and pull on the spout, taking it straight out. You'll now see a copper supply pipe in the wall.
If there's no set screw on the underside of the faucet, the spout should be threaded right into the supply line. Using a pipe wrench, slowly and firmly turn the spout counterclockwise to remove it from the wall. Take it to a plumbing supply store and request a replacement.
Replacing the Shower Diverter Knob
Once you get the new part home, attach the spout back to the wall, but don't tighten it. The purpose here is to anchor the spout, which makes the repair easier. Turn the faucet upward and pry apart the plastic prongs. Pull out the old metal shower diverter and slip the new one in its place.
Next, reinsert the diverter's underside portion by first putting in the spring and then the black washer. Now you can turn the spout right side up and tighten it against the wall. Turn the water back on and see if it works.
Replacing the Tub Faucet
If you're unable to find a new diverter knob, you may have to replace the tub's faucet. It should be removed in the same way as before and brought back to the store so you can buy the correct replacement. If the spout is threaded, these threads have to be running in the same direction as the old one.
Reattach the spout to the wall and try using the diverter again. If this doesn't fix the problem, you may have to remove the faucet and repair or replace the internal water diverter valve.