For many printers, the ability to add the printer via the Print & Scan > Default Add Printer view relies on the Bonjour service. This service advertises the printer on your local network and makes it possible for the Mac to "see" it. With the Epson not appearing in this Add Printer view it could indicate that the service has failed or something is blocking it. A quick action would be to turn the printer off for a minute and then back on again. With the printer back on, you can then open Safari, select the Bookmarks icon in the toolbar and then select the Bonjour entry in the sidebar. If the Epson is broadcasting its existence on the network then an entry should appear in the top right pane of Safari with Bonjour selected. If there is no sign of the printer then it may need repair.
Thanks for your information. It would appear that Bonjour is not being recognized by the printer. Is there a way to remedy the Bonjour situation at all? Otherwise, is it the printer that is the issue? It's not even two years old and this just happened (for no apparent reason). Is it likely that something has interfered with Bonjour's technology?
Just wondering if there's anything else I should or could do to remedy this. In the meantime, I have the printer working just fine with a USB connection. Not what I prefer, but it will do... for now.
It would be unusual for only Bonjour to stop working in the printer. The more likely is that the printer is set to a different network subnet to that for your Mac or, as you mentioned, something like a firewall is blocking it.
The IP addressing is the most common cause. If there is a process to view or print the network settings for the Epson, then this will show what IP address range it has, which should be the same as your Mac. With the IP address, there will be four sets of numbers. For a typical home network, the first three sets are known as the IP subnet, while the last set is the network address. For example, a device with an IP address of 10.0.1.5, has an IP subnet of 10.0.1 and a network address of 5. For your Mac to 'see' the printer, both devices would need the same IP subnet, while having a different network address. So if you can check what IP address the Epson has, you may find it is using a different IP subnet to your Mac.