Can't make PHP code to work

I have two list (integer) fields. I want to alert the user if the total is over a certain limit. Nothing I do within the PHP code window produces an error even if I write this:

if(4 > 2){
  $this->set_error();
}

I imagine the real code would look something like this:

if($this->value + $this->entity->field_other_field['und'][0]['value'] > 4 ){
  $this->set_error();
}

But as I said, the php code doesn't produce errors on the page. Other validation options work on the page so I know this isn't a larger issue with module config.