Faulty Explora

Every few seconds (like clockwork) my picture freezes for a moment and then jumps forward again. When I reboot the Explora the problem vanishes and the picture is perfect again, but when I turn on the TV the following day it is back. I therefore have to reboot my Explora every evening before I watch TV. My software updates are up to date. The call centre cannot help me. This has been going on for months on end. I want my decoder to be replaced.