Once it starts failing every show fails until a reboot.
There was a series finale of supernatural. It was two parts. It recorded the first part fine. It went to switch to the second one and the failure occurred on all 4 tuners (two HVR-1800's - 2 HD, 2 std def). It was down all weekend. When I go to the guide and select anything I get the generic "no tuners available" sort of message.