Why am I not jumping?

I currently have a character controller and this script attached but I'm not sure why I'm unable to jump higher? It plays the animation fine but whenever I increase the Jump on the inspector it doesn't affect anything.

 using UnityEngine;
 using System.Collections;
 
 public class Player : MonoBehaviour {
 
         private Animator anim;
         private CharacterController controller;
 
         public float speed = 600.0f;
         public float turnSpeed = 400.0f;
         private Vector3 moveDirection = Vector3.zero;
         public float gravity = 20.0f;
     public float jumpSpeed = 8.0f;
 
 
     void Start () {
             controller = GetComponent <CharacterController>();
             anim = gameObject.GetComponent<Animator>();
         }
 
         void Update (){
 
         anim.SetFloat("horizontal", Input.GetAxis("Horizontal"));
 
             if (Input.GetKey ("w")) {
                 anim.SetInteger ("AnimationPar", 1);
             }  else {
                 anim.SetInteger ("AnimationPar", 0);
             }
 
             if(Input.GetKey ("s"))
         {
             anim.SetInteger("AnimationPar", -1);
         }
 
 
 
         if (controller.isGrounded && Input.GetButton("Jump"))
         {
             moveDirection.y += Mathf.Sqrt(jumpSpeed * -3.0f * gravity);
             anim.SetTrigger("isJumping");
             
         }
             else if(Input.GetButtonUp("Jump"))
         {
             anim.ResetTrigger("isJumping");
         }
 
             if(controller.isGrounded){
                 moveDirection = transform.forward * Input.GetAxis("Vertical") * speed;
 
             }
 
             float turn = Input.GetAxis("Horizontal");
             transform.Rotate(0, turn * turnSpeed * Time.deltaTime, 0);
             controller.Move(moveDirection * Time.deltaTime);
             moveDirection.y -= gravity * Time.deltaTime;
         }
 }
 

Anyone have any idea why this isn't working? Thanks