Can I consolidate an existing consolidation loan?
Yes, under three conditions:
Borrowers can consolidate existing consolidation loans into a new Direct Consolidation Loan if they include at least one other FFEL or Direct Loan into the new consolidation loan.
Borrowers can consolidate a single Federal Consolidation Loan if the loan is in default status or has been submitted to a guaranty agency for default aversion by the loan holder.
Borrowers can consolidate a single Federal Consolidation Loan if they intend to apply for loan forgiveness under the Public Service Loan Forgiveness Program.
Borrowers who have only a Direct Consolidation Loan cannot consolidate again unless they include an additional loan.
Source: U.S. Department of Education