How to make a character controller jump properly

The code i am using made it successfully jump and move but sometimes it dosent jump when i press the space bar and some times it does. It always says that it sets vertVelocity to 5 ish when i press the space bar when i printed it with debug.log but it dosent jump i need some help everything else works fine though.

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class FPSController : MonoBehaviour {

 public float speed = 2f;
 public float sensitivity = 1f;
 public float jumpForce = 5f;
 public Vector3 Movements = new Vector3(0, 0, 0);

 private float vertVelocity = 0f;
 private float moveH;
 private float moveV;
 private float rotX;
 private float rotY;
 private int jumpCount = 0;

 public GameObject cam;
 private CharacterController player;

 private void Start()
 {
     player = GetComponent<CharacterController>();
 }

 private void Update()
 {
     moveH = Input.GetAxis("Horizontal") * speed;
     moveV = Input.GetAxis("Vertical") * speed;
     rotX = Input.GetAxis("Mouse X") * sensitivity;
     rotY = Input.GetAxis("Mouse Y") * sensitivity;

     Vector3 move = new Vector3(moveH, 0f, moveV);
     move = transform.rotation * move;

     transform.Rotate (0f, rotX, 0f);
     cam.transform.Rotate(-rotY, 0f, 0f);
     player.Move(move * Time.deltaTime);

     if (!player.isGrounded)
     {
         vertVelocity += Physics.gravity.y * Time.deltaTime;
         vertVelocity = Mathf.Clamp(vertVelocity, -53f, jumpForce);
         Movements.y = vertVelocity;
     }
     else
     {
         vertVelocity = 0f;
         if (Input.GetButtonDown("Jump"))
         {
             vertVelocity += jumpForce;
             vertVelocity = Mathf.Clamp(vertVelocity, -53f, jumpForce);
             Movements.y = vertVelocity;
         }

     }
     player.Move(Movements * Time.deltaTime);
 }

}