How to trigger Form Validators in Angular2

I don’t know if you are still looking for an answer, so here is my suggestions:

Have a look at this: Angular 2 – AbstractControl

I think what you could do is following:

this.formGp.controls['checkboxFld'].valueChanges.observer({
    next: (value) => {
       this.formGp.controls['numberFld'].updateValueAndValidity();
    }
});

This should trigger and run the validators. Furthermore the state gets updated as well. Now you should be able to consult the checkbox value within your validator logic.

Validaton-Guide

FormControl Documentation