Replacing a Broken Knob

• 1). Determine the extent of the damage. If the broken knob rotates smoothly, still turns the shower on and off properly and doesn't drip, replacement may be limited to the knob itself.
  
  
• 2). Pry the plastic center cap out of the knob with a small screwdriver.
  
  
• 3). Unscrew the Phillips-head screw that secures the knob to the valve stem. Pull the knob straight off the stem and take it to a home improvement center or plumbing supply company for a universal replacement.
  
  
• 4). Use a hacksaw to cut off the broken knob if it is frozen on the valve stem due to corrosion. Excessive force should be avoided because of the risk of damaging the valve cartridge or seals. Most stuck plastic knobs can be removed by making a lengthwise cut down to the valve stem, inserting a thin screwdriver into the cut and splitting the knob down the middle.
  
  
• 5). Clean the corrosion off the valve stem splines and apply petroleum jelly.
  
  
• 6). Press the new knob on the stem and secure it with the single Phillips-head screw. Install the plug over the screw head.
  
  

Shower Valve Cartridge Replacement

• 1). Replace the valve cartridge after removing the shower knob if dripping has been noted or if the shower does not turn on and off properly with the knob.
  
  
• 2). Turn off the water supply to the house.
  
  
• 3). Remove the escutcheon plate covering the valve body.
  
  
• 4). Lift the retaining pin securing the cartridge in the valve body by grasping the nub of the pin with a pair of needle-nose pliers and pulling straight up.
  
  
• 5). Use a universal cartridge puller, available in the plumbing department of hardware stores and home improvement centers, to remove the cartridge.
  
  
• 6). Place the hollow end of the cartridge puller over the existing cartridge. Secure the cartridge puller to the cartridge by inserting a screw into the hole in the end of the valve stem. Engage the ears of the puller with the ears of the cartridge and rotate the puller to extract the old cartridge.
  
  
• 7). Insert the replacement cartridge straight into the valve body with the ears on the cartridge at the 12 o'clock and 6 o'clock position.
  
  
• 8). Slide the retaining pin down to lock the new cartridge in place.
  
  
• 9). Replace the escutcheon plate. Press the new knob on the valve stem and secure it with the single Phillips-head screw in the end of the stem. Install the plug over the screw head.
  
  
• 10
  
  Turn the water back on and check for leaks.