I also have a G4 router where I can set the channel through the web interface, and I set it to "2". I then reset the Decos and recreated a new mesh network, with the G4 router already up and running....

@Bahamas Thank you again for your response. I have used NetSpot on my Apple devices: after turning off 5GHz for the "Guest" account, it no longer shows up in listings anywhere. Out of curiosity, I...

@Alexandre. Thank you for your immediate response. When I turn on the Guest network (with its own SSID), it shows up in the list of networks. When I then limit it to 2.4 GHz, it drops off the list....

The 3-Unit Deco system does not appear to provide 2.4Ghz band WLAN, although both /2.4 and 5 GHz) are turned on: I want to connect an IOT device (smart thermostat) which only uses 2.4 GHz - no luck....