Yes, unfortunately. This has been reported and we are informed the iPlayer launches if signal is low.
I understood a fix was being pushed out late last week to fix this (did this happen @Karl-TalkTalk ), so it may be worth checking your updates available under settings or a reset of the box by pressing the button on the left hand side of the box 5 times until it restarts. You will lose recordings if you use this facility and have to sign into catch up services again, but if an update is pending it will be installed.
The advice is to use channels 101 and 102 which work normally and if you have an HD or 4k TV the picture is much sharper.
Hope this helps
Please remember to mark Solved Posts with Best Answer. Doing so helps other customers and saves TalkTalk's Support Team time by only looking at unsolved topics. Thanks, Steve (a fellow customer).
