Failover for specific virtual server

Hi VictorRuiz , 
you can do it by HA score configuration , Configure it for the pool that assigned to required virtual server. 
I see there is no difference to failover based on virtual server status (UP/Down) because if the virtual server’s pool became down , all traffic destinated to this virtual server would be resetted and F5 marks the virtual server down. 
so I see you can confugure HA Group Score. 
to configure it follow these article : 
https://support.f5.com/csp/article/K42542000
in this article you will find the videos that mihaic sent to you , and I think that this is the only way to meet your requirement. 
I want to add. 
> you can Isolate your configuration by creating 2 traffic groups , one for virtual server B and C whereas the other for your targgeted virtual sever A , let we name it (Virtual_server_A traffic group) . 
> you will create new 2 floating ips address for traffic group 2 and put both of  them in Virtual_server_A traffic group , both of floating ips from external and internal vlan subnet respectively ( i mean client/server sides) to  listen and forward traffic for the Virtual_server_A traffic group. 
also go to (local traffic >> virtual address >> and put your targgeted virtual server A on Virtual_server_A traffic group.
> you can make this traffic group (Virtual_server_A traffic group) Active on the main F5 node with the other traffic group ( virtual server B , C ) , I mean both of traffic groups will be active on one node. 

> until here , I did not make any differnece only created  new traffic group "Virtual_server_A traffic group" and two floating ips (one for client side from external vlan subnet and the other from server side from internal vlan subnet). 

> After that  follow mihaic  video or article K42542000 , as you will  go to newly created traffic group (Virtual_server_A traffic group) and configure change its options to failover based on HA Score and create an new HA group score based on Pool and give it a score. 

> the effect of this , you will isolate your issue and get a more granular control on "virtual server A" far from the rest of other virtual servers. 

Regards.