First try powering off the ONT, router & any other TT equipment for a full thirty minutes.
Do you have the Eero & Grandstream ATA or the Hub 2? If the former, try disconnecting the Eero & connecting the Grandstream directly to the ONT in place of it. Then reset the Grandstream. If all is now OK, connect everything back as it should be.
From the 29th of March our TalkTalk Community will move to peer-to-peer support and the TalkTalk team will no longer be here to support with queries. Don’t worry we still have plenty of ways to reach out if you need to speak to TalkTalk directly. For more details check out the link here
How to contact TalkTalk Broadband - TalkTalk Help & Support
