VIRGIN TIVO BOX PROBLEM

I have been experiencing some problems of late when i set it to record , It does`nt happen with all recordings but about every 3rd one. The red light comes on to say it is recording but when i go to watch the program back there is nothing there.
When i go into "recording hiccups" it says "The program was not recorded because the video signal was unavailable"
When i spoke to Virgin they advised rebooting the box on a weekly basis to avoid future problems.
Has anybody else had the same or similar problem ?

Thanks.