Hi Andy,
Check your SAPXPG_DBDEST_<DATABASEServer> RFC connection is working properly. This is under TCP/IP Connection. If you are using Windows check ATAMAN or similar software whether entries are correct. As others have mention executing sapdba_role in database server is important. Other than that you should also schedule other housekeeping jobs running under DB13 make sure those are running fine.
All the best,
Zaki