<button
    [disabled]="!questionsForm.valid || noWards.length < 3"
    [ngClass]="{'default':!questionsForm.valid}"
    (click)="goToNextStep()" class="contact100-form-btn">
      <span>
        Start
        <i class="fa fa-long-arrow-right m-l-7" aria-hidden="true"></i>
      </span>
    </button>

this.questionsForm = this.formBuilder.group({
            new: ['', Validators.required],
            noWards: ['', Validators.required],
            user: [''],
            pass: ['', Validators.required]
          });