Getting error "The search request was unable to connect to the Search Service" In SharePoint 2016

Hi,

I am getting error on SharePoint site  on search page as " The search request was unable to connect to the Search Service. " When I tried to restart SharePoint Search Service in Central Administration, I am getting error as "Invalid search service unprovisioning: application 'Search Service Application' still has a ready component 'in search service instance' on server " 

Please advice the solution

Thanks,