When your certificate is issued you will receive 3 certificates: Yourdomain.crt ComodoClass3SecurityServicesCA.crt GTECyberTrustGlobalRootCA.crt
Add the ComodoClass3SecurityServicesCA.crt certificate as Trusted Roots:
Then attach each certificate in turn to your website's Key Pair in the following order. At this point your Key Pair will be black.: Yourdomain.crt Intermediate CA certificate Root certificate
Your Key Pair will now turn green.
Stop and Start the server, your site can now be found using the https entry