If you want to check if fields are filled in you might be better using jQuery and JavaScript for that.
For example you could have a button that looks like a submit button that call a JavaScript function on click like
<button type="button" onclick="submitForm(this) ;" class="btn btn-primary" data-form="formId">Submit</button>
<input type="hidden" id="submitGo" value="true" />
(Note - the submitGo has deliberately only got an id attribute and no name attribute as it's only used by the JavaScript checking process)
and then a JavaScript function like
<script>
function submitForm( item )
{
form =jQuery(item).data("form")
jQuery("#"+form+" input").each (
function()
{
if ( jQuery(this).val () = "" )
{
jQuery("#submitGo").val("false") ;
return false ;
}
}
) ;
/*create similar functions for select/textarea if in the form*/
if ( jQuery("#submitGo").val() != "false" )
jQuery ("#"+form).submit() ;
}
This way your not constantly submitting the data getting the server to check it and constantly reloading the page - the basic checks are being done at the client end (also important to remember when using jQuery in Joomla you have to use full jQuery not $) and if you do add JavaScript add it with joomlas addScript functions so it can put the script into the header properly.
Also if you have Bootstrap 3 loaded BS3 has its own "required" functions that just need certain classes adding to the form/inputs you want as required. Search Bootstrap 3 form required for more info on that one.