How to Identify and Replace Your Delta Monitor Shower Cartridge (Old vs. New)

The first and most critical step is to completely shut off the water to the shower. Locate the main water shut-off valve for your home (often in the basement, a utility closet, or outside near the meter) and turn the handle or knob clockwise until it is fully closed. If your shower has dedicated shut-off valves (sometimes accessible via a panel behind the shower wall), you can use those instead. After turning the valve, go back to the shower and turn the handle on to drain any remaining water and confirm that the supply is off. No water should be flowing.

Begin by removing the faucet handle. Look for a small set screw, often located on the underside of the lever handle. You may need to first pry off a small decorative cap with a small flathead screwdriver to access it. Use the appropriate Allen wrench or Phillips screwdriver to loosen the set screw (counter-clockwise) until the handle can be pulled straight off. Next, remove the large, tube-like trim sleeve by pulling it straight off the valve. Finally, remove the faceplate (escutcheon), which is typically held on by two screws. Unscrew these and set the plate aside.

With the trim removed, you will see a large brass or chrome nut, called the bonnet nut, threaded onto the valve body. This nut holds the cartridge in place. Using a pair of channel lock pliers or a pipe wrench, grip the nut firmly and turn it counter-clockwise to loosen it. If the finish is decorative chrome, wrap a cloth or rag around the nut before gripping it with the pliers to prevent scratching. Once loosened, you should be able to unscrew it the rest of the way by hand.

Grip the stem of the cartridge with pliers and pull it straight out of the valve body. It may be stuck from mineral buildup; if so, wiggle it gently from side to side while pulling. If it won't budge, use a dedicated cartridge puller tool to remove it without damaging the valve. Once removed, identify the cartridge type. The older Delta Monitor 1300/1400 series cartridge (model RP19804) is typically gray with a solid, round body. The newer MultiChoice Universal Valve cartridge (model RP46074) is typically white and has a more complex, squared-off shape. Note the orientation of the cartridge and the location of the 'H' marking on the valve body (usually on the left) for correct installation of the new part. Take the old cartridge to a hardware store to find an exact match.

Before inserting the new cartridge, inspect the inside of the brass valve body. Use a cloth or a small nylon brush to clean out any sediment, mineral deposits, or pieces of old rubber O-ring. Take the new cartridge and apply a thin layer of plumber's grease to all of its rubber O-rings. This lubricates them, making installation easier and helping to create a perfect seal. Align the new cartridge correctly. Look for the 'H' marking on the side of the cartridge and make sure it aligns with the hot water inlet on the valve body (typically the left side). Carefully push the cartridge straight into the valve until it sits flush and is fully seated.

Thread the bonnet nut back onto the valve body by hand until it is snug. Then, use channel lock pliers to tighten it an additional quarter-turn. Do not overtighten, as this can crack the cartridge or the valve body. Slide the trim sleeve back over the valve, reinstall the escutcheon plate with its two screws, and reattach the handle. Tighten the set screw on the handle with your Allen wrench or screwdriver until it is secure.

Go back to the main water shut-off valve and turn it on slowly (counter-clockwise). Return to the shower. With the handle in the off position, visually inspect for any drips around the handle, bonnet nut area, or escutcheon. Listen carefully for any hissing sounds. If all is dry, turn the shower on. Test both the hot and cold water functions, rotating the handle through its full range of motion. Check for leaks again while the water is running. If you find a leak, turn the water off and re-check that the cartridge is seated properly and the bonnet nut is snug.