Cartridge valves are one of four types of valves that you'll find inside a faucet, and they are particularly well-suited for shower faucets. A cartridge has holes that regulate water flow and temperature when you turn the handle, and it offers more precise control than other types of faucets. One of the advantages of cartridges is that they are easy to replace, assuming mineral deposits and corrosion don't hamper your efforts.

Accessing the Cartridge

No matter what model of faucet you have, it's essential to turn off the water supply before you disassemble it, or you could be scalded. After that, you must figure out how to disassemble it, and that isn't always easy. The cartridge is behind the handle, but the fasteners holding the handle are seldom in plain view. If you can't find a cap hiding a retaining screw, look for an Allen nut in an inconspicuous place, such as under the lever. Once you find the fastener and remove it, the rest is easy. The handle should come off effortlessly.

Removing the Cartridge

In theory, after you remove the temperature limiter -- a notched plastic disk -- from the valve stem and you pull the pin holding the valve with needle-nose pliers, you should be able to pull the cartridge straight out. In reality, the procedure is often complicated by the fact that corrosion and mineral deposits have locked the cartridge in place. You may need a cartridge puller, which is somewhat like a corkscrew for cartridges. Before you pull the cartridge, be sure to note its orientation as you will have to insert the replacement in the same orientation.

Assessing the Need for Replacement

Difficulty regulating temperature or water flow is an indication that you need a new cartridge, but it could also mean the old cartridge is simply blocked by mineral deposits. If it's the latter, you should be able to see the deposits. Soaking the old cartridge in vinegar will probably dissolve them. If you see cracks or gouges, however, it's time for a new cartridge. Leaks are usually caused by worn washers in the valve seat or O-rings around the body of the cartridge. To fix a leak, you usually replace the washers and O-rings -- not the cartridge.

Inserting the Replacement