A pin whose movement triggers setting of the borehole tool, is initially held by a collet that is supported off a surrounding housing. A spring is supported off the pin and would push a housing that locks the collet to the pin axially to unsupport the collet but for the presence of a Kevlar® wire that has an associated heater. The wire pulls the housing that locks the collet against the spring bias and has an end attached to the pin. Melting the wire allows the spring to move the housing that traps the collet to the pin. At that point hydrostatic pressure can move the pin to either open a port on the borehole tool to set it hydrostatically or to move an actuation rod attached to the pin to set the borehole tool mechanically or with a combination of mechanical and hydraulic force.