Installed Letsencrypt SSL reports says "F" Rating.

Thanks for a great control panel.I Switched over from VestaCP to Centos Web panel and already loving this.

I have installed Letsencrypt and it worked smoothly. SSL got installed. But when I checked the quality of SSL then I found that its saying "F" Rating.

What can I do to get A+ Rating? Please help.

check this

http://forum.centos-webpanel.com/ssl/short-let's-encrypt-guide-on-centos-6-x/msg6629/#msg6629