Finally found a solution..
1. Open SQL Server Configuration Manager
2. Select SQL Server Network Configuration
3. Select Protocols for [named instance]
4. Select IP Addresses tab
5. For each IP in the list, delete 0 from TCP Dynamic Ports and enter 7201 in TCP Port field below
6. One IP entry will have an IP address for the SQL Server - set this to Enabled and Active
7. Click Ok
8. Repeat steps 3 to 7 for another instance using port 7202
9. Open Firewall from Windows Control Panel
10. Advanced Settings
11. Add Inbound Rules based on Port:
> Name 'My Instance SQL Server', TCP, port 7201
> Name 'My Other Instance SQL Server', TCP, port
> 'Native SQL Server', TCP, port 1433
> 'SQL Server', UDP, port 1434
12. Restart services
13. Ensure SQL Server Browser service is started