Why are my welded parts not moving?

I already tried to fix it and looked in wiki but I couldn't find the error, the two parts are succesfully getting welded but it won't move. So the problem is that it doesn't moves.

wait()
local Weld = Instance.new("Weld")
Weld.C0 = script.Parent.CFrame:inverse() * script.Parent.Parent.Union.CFrame
Weld.Parent = script.Parent
Weld.Part0  = script.Parent
Weld.Part1  = script.Parent.Parent.Union

--The problem:
repeat wait()
    Weld.C0 = Weld.C0 - Vector3.new(0, 0.1, 0)
until script.Disabled == true

I want to keep the parts anchored, when I unachor only Part1 is moving.