sky receiver?

My Amstrad sky receiver works for about an hour then just switches itself off, it then takes about a 30 seconds before I can power it back up and then more time to return to the channel I was watching.
The frequency of these switch offs then increase until it is happening every few minutes. Its not anything like low remote battery power and the same fault occurs even when operating direct from the receiver. It is not a mains input loss but merely a fault that returns the system to standby.