Grohe manufactures several signature lines of taps for high end homes and residential properties. Grohe taps rely on a replaceable cartridge system that you must replace every three to five years or as needed. The Grohe cartridge controls water pressure for the tap as well as the mixture of hot and cold water. As the tap cartridge ages and builds up with lime and other minerals, the tap may leak or start dripping while the tap is in the "off" position.
Shut the handles for the water main off. Locate the handles (either one or two) connecting to rigid copper piping or flexible metal tubing, and turn these (left) counterclockwise 1/4 turn to reach the "off" position. The water main is located underneath the cabinets of the room you are working in.
Insert the Allen key into the star-shaped aperture located beneath the Grohe tap spigot. Turn the wrench counterclockwise until the handle comes off the spigot (4 to 6 rotations).
Remove the tap handle from the assembly. This will allow you to access the cartridge system located directly beneath the handle.
Grasp the cartridge firmly with your pliers, turning it counterclockwise until you hear a clicking sound, signalling that you have unlocked it from the cartridge assembly.
Remove the cartridge. You may need to use the pliers for leverage to remove the cartridge.
Insert the new cartridge into the assembly, using your pliers to turn the cartridge 1/4 turn clockwise, locking it into place.
Reattach the Grohe tap handle, using the Allen key (clockwise) to tighten it into place. Make sure it is as tight as you can make it by hand without stripping it or using a tool, which may damage the tap.
It is not always necessary to replace the cartridges in a Grohe tap with new ones. Soak your old cartridge in a mixture of vinegar (10 per cent) and water for several hours until it has dissolved most of the deposits on the cartridge, and brush it with an old toothbrush or wire metal brush. Once it has been properly cleaned, you may reuse the cartridge until it develops cracks.
Always shut the water main off for the room you are working in when performing plumbing tasks. Water lines are filled with hot and cold water under significant pressure, and damage to these lines can result in serious damage or injury to you.