Jamesbo
From memory, for my model, you must have the Intellipanel in HOURS mode (where you see the number of operational hours) and THEN press and HOLD BOTH the buttons down simultaneously for two seconds. Then the wrench goes away.
I haven't done a scientific study, but my belief is that the SERVICE INDICATED light (wrench) comes on at EACH 50 hours.... not 50 hours from the reset point, but everey 50 hours... so, it may turn on "early" for the next service.