To install the execution server in silent mode please run the following command, 

WindowsExecServer.exe /s /f1"[PATH_TO_INSTALL_ISS]Install.iss" /v"/qn PROP_LANGUAGE=<LANGUAGE>"  

Example:

WindowsExecServer.exe /s /f1"c:\temp\Install.iss" /v"/qn PROP_LANGUAGE=EN"  

The file "Install.iss" is attached, this file should be copied into directory "[PATH_TO_INSTALL_ISS]" before executing the silent installation mode.

To check, if the silent installation of execution server was successful, there should be a file after installation named "setup.log". For a successful installation, it's content should like the following:  

[ResponseResult]   ResultCode=0  

Resultcode=0 indicates a successful installation, other result codes indicate a failure.