Intermittent no signal

[spireman123]

My Sky HD box has started getting intermittent no signal. Usually on BBC1, BBC2, ITV and Channel 4. Signal on Input 1 has no strength and no quality, the Input 1 Lock indicator says not locked and Input 1 Network ID/Transport System says null. Input 2 is fine. 

I am reluctant to pay £65 for an engineer to come out.

Any ideas?

Thanks in advance.

[spireman123]

Just to add, Channel 4 came back and signal on both Input 1 and Input 2 are fine now.