Xfinity internet. Ethernet OK, wifi not showing in list of networks

Just had installation here this afternoon.  Verified that ethernet connection worked and that the new network was listed in list of available wifi's.  A few minutes after the tech left the wifi was not longer showing in the list as I attempted to set up additional devices to access the network.  Ethernet works, but no sign of wifi. I have rebooted the gateway and router multiple times to no avail.  Still not showing in wifi list.