Angular checkbox with boolean

I'm working on a Angular project where I need to give an use admin right. The isAdmin is a boolean (false/true). But it can't figure it how to parse the right value to the component and save the value.

<div class="checkbox">
   <label>
     <input type="checkbox" name="isAdmin" [(ngModel)]="user.isAdmin" [checked]="item.checked">
     Is Admin?
   </label>
</div>

The component.ts looks likes this:

this.userForm.get('isAdmin').valueChanges.subscribe(val => {
  this.newUser.isAdmin = !!val;
});

Can someone see what is mine mistake?