A shower cartridge is the part inside a shower valve that controls the flow of water to the shower head. The cartridge is connected to a single handle that turns to allow the blending of hot and cold water. How to you know when the cartridge becomes worn?
There are several signs of a cartridge needing to be serviced or replaced. The most obvious is that you have a drip or running water when you turn the handle to the off position. You may also get a drip at the handle itself. Furthermore, you may feel the handle getting increasingly more difficult to turn.
These conditions can be repaired easily enough. If you contact the manufacturer, they may send you free parts. The parts they send are new molded rubber parts that help the cartridge to seal. You will need to turn off the water to the house, remove the handle, and pull out the cartridge. From there you can replace the old rubber parts. Lubricate the cartridge and slide it back into the valve.
If you are going to install a new cartridge, you can follow the same steps above except that you obviously don’t have to worry about replacing the molded rubber parts since the new cartridge will have all new parts anyway.