Grohe Thermostatic Shower Valve Adjustment. A thermostatic valve mixes the hot and cold shower water to a predetermined and consistent temperature, hence preventing scalding and cold shock. If you have the directions that came with the trim the pictures will be about the same as this but it will be more specific to your valve.

Grohe 34902 3/4 thermostatic valve parts faucet shark inc. Basically, the thermostatic control is leaking; Position the jaws of the wrench over the top nut of the adjustment screw.