Abstract: A running tool is used to set a seal on a casing hanger in a wellhead. The running tool has a holder for connecting the running tool to the casing hanger as it is lowered into the wellhead. A piston is carried on the running tool above the seal. An actuating passage extends from an axial passage in the running tool to the piston. A release passage extends from the axial passage to the holder. A pin and slot enables the upper section of the tool to be lowered relative to the lower section. The combination of a sliding valve, moved by a plug pumped from the surface, and the pin and slot, places the running tool in a mode for setting the seal and a mode for releasing the running tool from the casing hanger.