Script only works one time?

Below works and all but it only works one time for some reason. Basically what it does it checks if something that touches it is a zombie and if it is it loses health from the zombie by -1 from a value that is displayed on a GUI. For some reason it subtracts 20 from it but when the zombie touches it again nothing happens.

function onTouch(part) 
    local h = part.Parent:FindFirstChild("Zombie torso")
 

wait(3)
    if h~=nil then
             for i, v in ipairs(game.Players:GetChildren()) do
	  local n = v.PlayerGui.Notice.Box.Health1.Health.Value
                n = (n -20)
                v.PlayerGui.Notice.Box.Health1.Text = n
              game.StarterGui.Notice.Box.Health1.Text = n



     end
end
end

script.Parent.Touched:connect(onTouch)