If when installing an HP 7520 WiFi printer with HP Easy Start you get a warning that the scanner does not support “Bonjour” then you end up with a working printer but no scanner!
In most cases this happens because you have a dual band router advertising 2.4GHz and 5GHz on the same SSIDs. In short the HP 7420 scanner only works with a 2.4GHz network.
The solution is to disable the 5GHz network or rename it and only connect the printer to the 2.4GHz SSID. This may have to be done manually. Once WiFi connected uninstall the HP printer software using HP Uninstaller and reinstall the printer using HP Easy Start. This time you get no scanner warning message and have both printer and scanner working.