HomeHub 6 had a problem with ChromeCast - resolved by Google help.
I recently switched broadband and TV providers from Virgin to BT. My elderly (v1) ChromeCast had worked fine with Virgin, but refused to work with my new BT HomeHub6. I could set up Chromecast ("Living Room") with my phone, but when I tried to cast, it reported "no compatible devices found".
He advised me to reset my router (HomeHub6) by switching it off for 30 seconds and then switching on again. (This apparently clears out something in the router which is bocking ChromeCast from working.)
And - hey presto - Chrome cast now works perfectly.
I hope this simple trick might help anyone else with a similar problem.