html2pdf not working properly

Question

I am using Codeigniter HMVC structure.When i will put limit in my query with 375 than its working properly but if i will remove that limit than html2pdf is giving me blank pdf

I tried to debug for that but i can't get what is going on ? I just came to know parsingHTML.class.php have function with name setHTML which is giving me blank

Code :

 public function setHTML($html)
    {
        // remove the HTML in comment
        print_r($html);exit;
        $html = preg_replace('/<!--(.*)-->/isU', '', $html);
        print_r($html);exit;
        // save the HTML code
        $this->_html = $html;
    }

IF i will echo before preg_replace than i can see html page and after preg_replace its giving me blank html.

My html page is very large so may be that cause the issue ? if yes than anyone please provide me debug points or something to check the issue?

Any suggestions to check any other places or debug points ? Please help me. Thanks in advance.