Abstract: An apparatus for stopping the flow of water through the opening in a fire sprinkler head after the failure of an originally installed triggering device, which apparatus thereafter serves as a substitute triggering device. The apparatus is provided with a meltable body portion having a first bore formed therein with a shoulder formed at one end of the first bore and a second bore formed generally transverse to and in contact with the first bore at the shoulder end of the first bore, a spring positioned in the first bore, a piston positioned within the spring and having a slot at one end which is alignable with the second bore and a pin inserted through the second bore and engaging the piston slot. Thus, after placement in a sprinkler head, transverse movement of the pin results in the release of the piston which is moved by the spring into the sprinkler head opening, stopping the flow of water.