As you know, ConfigMgr 2012 is supported on a SQL named instance. However, in this scenario when you try to install a primary site that will be joined to a Central Administration Site (CAS), you can get the following errors :
In ConfigMgrSetup.log :
Cause:
ConfigMgr 2012 requires SQL Server to use static port TCP/1433 and TCP/4022 for SQL Service Broker if using a CAS. Since SQL Server named instances default to dynamic ports, if you are using named instances, you must manually reconfigure the named instance to use static TCP/1433.
Solution:
You need to configure SQL Server to listen on a specific TCP Port (1433). Look at this link.
Ed Price - MSFT edited Original. Comment: Title and tags