SP2016 search issue.

@Rafik: Can you confirm u have single server or multi server farm... Still I couldn't figure out on this issue. We have sp 2016 test environment with single server there search is working fine. But while creating the web application in front end server and search service application running on app server, search is not working. I have checked crawl is fine without any error even I can see the certain amount of as searchable items... but while searching something after processing for long time throwing time out error.... I have tried creating second service application still didn't work.... Is there anything on network level like port connectivity between the server I can look into.... Appreciate any help on this.

I had already a similar problem, I resolved the issue by removing the corrupted service and creating a new Search Service application.

Is index reset feasible for you? If yes, please try.

Crawl log is fine no errors.... but while searching for anything on in the site.... It's keeps rotating the page Bar....then it says request timed our error getting... Can someone please help me on this how sharepoint 2016 search can be brought up..... any standard documents available which service should run on which server..

Did you check the crawl log for errors? Does your web app getting crawled propely?

Communication between server should be free, i think as minimum you have to open the port from both side.

It seems there is issue with opening 808 port no... as per msdn to work with search 808 port should be opened.. so my question in which server I should open this port, app or wfe??? By d way I am using sharepoint 2016 which has application with search and wfe server. Search service application has been configured in app server.

Looks like search service is unable to connect your WFE, try to login on App server using the Search service account then browse the Web application (wfe ) and see if you can do it?

Can you check the EventViewer and ULS Logs?