pause the 5G side of wifi

Xfinity Wireless Gateway Admin Tool

While many find that My Account, xFi and X1 are their preferred tools for accessing WiFi information, you may also wish to use the Xfinity Admin Tool if you are a more advanced user.

1. Connect a laptop, computer or mobile device to your home Internet network either by WiFi or an Ethernet cable that is connected directly to your Wireless Gateway.
2. Open a web browser and go to the Admin Tool (http://10.0.0.1). This is the wireless gateway's administration site. The default settings to access the Admin Tool are:
   • Username: admin
   • Password: password (case-sensitive)
3. Click Login.
   Note: If you previously changed your Admin Tool password, you will need to use your new login information. If you don't remember your Admin Tool password, you will need to factory reset your Wireless Gateway.
4. On the left navigation menu, select Gateway, then Connection and then WiFi.
5. Under Private WiFi Network, you'll see the Name (SSID) of your WiFi network.
6. After making changes, click Save Settings.

I was having similar problems. In my case the 2.4g was turned off. Basic tech support could not help me. By pure accident what fixed the problem was enabling bridge mode followed by disabling bridge mode again. You need an Ethernet connected computer for this. You loose WiFi when you enable bridge mode.