Grohe shower taps are preset at the factory to allow for a maximum hot water temperature setting. This setting is actually related to the position of the handle, as it controls how far open the hot water valve is and, therefore, how much hot water is mixed in with the cold. The homeowner can adjust this setting to reduce the maximum hot water temperature. The process requires little plumbing knowledge, but some experience in fixing appliances or doing normal repairs certainly helps.
Turn off the water to your shower tap.
Remove the handle to the shower tap. Remove the small screw under the lever handle with an Allen key or Phillips head screwdriver, depending on what type of screw is present. Slide the handle back and off the tap.
Remove the temperature control knob, which is the round, dial-shaped fitting over the tap cartridge. Put the manufacturer-supplied adaptor on the cartridge. Line up the lever stop pin with the arrow symbol on the cartridge.
Turn on the water and rotate the adaptor to the left, or counter-clockwise, until the water temperature is at the level you want. Take note of the number to which the adaptor points.
Shut the tap off by turning the adaptor to closed and line up the limit stop dial with the number you noted previously.
Assemble the tap by replacing the temperature control knob and handle, then tighten the handle screw. Turn on the water and operate the tap. If the temperature is not set properly, repeat as necessary until you achieve the right setting.