Frank,
a spring gets it's strength from the fact that its steel and, more important to this conversation, its shape.
Simply re-heat treating a spring won't make it have more spring force in the throw/travel you are using it in. You need to reshape it to gain more force or make a stronger spring if it exceeds the limits of the spring.
If the spring used to have adequate force and it now doesn't, it probably yielded (took a set/bent) and needs to be re-formed to it's original shape. That may require annealing, re-forming, then heat treating to proper hardness, then tempering.
