If your printer is dropping its WiFi connection with your router then you may have to tweak your enviornment a little. WiFi disconnections normally happen for two reasons. Either the printer is falling asleep and the router is naturally cleaning up its unused IP addresses or there is interferance causing a more natural DC.
Considering you already tried shutting down all WiFi equipment and can still reproduce the problem then I would say this is more of a sleep mode conflict between your printer and the router. One solution may be to adjust the sleep mode on your printer to either disable or extend its sleep period. Another simple test would be to rig up a ping test to keep the connection alive and active from the routers stand point. While I generally do not suggest disabling sleep mode you could also experiment with that option too, assuming your printer can even disable that feature to begin with. One last shot would be to update the firmware on the printer just incase it is not already up to date.
You may also want to reconsider how you have your printer network connected at the moment. If WiFi continues to give you problems then perhaps it would be best to string a LAN cable from the router to the printer instead. You can still have your PCs connect to the router over WiFi but this would eliminate a WiFi interferance situation from the printers troubleshooting perspective. Otherwise you could try swapping your router out with a different model in hopes of it being able to handle your printer better.