The only reason for asking about SD/HD was that digital TV platforms (of which VM is one) broadcast channels in clusters (known as multiplexes) which don't often bear any resemblance to their EPG positions. A signal fault affecting one broadcast TX is likely to affect all the channels on that frequency, so there may be commonality. It won't help progress the fault, but you can check QVC Style SD & Pick SD, both of which are FTV, and co-muxed with Sky Max SD (which I assume is what you mean by referencing Sky One)
Anyhow, I think the official answer would be that if you have any self-installed cabling, some eyes of suspicion would fall on that first. Certainly I'd imagine the VM tech would want to check all your cabling end-end, and if the "self-install" bit is at all suspect, may want to replace that with VM-supplied co-ax. Officially all of VM's cabling forms part of their network, and should only be installed & maintained by them.
Call it in, or wait on here for a VM response... but either way, it'll need "hands & eyes" physically on your kit, which can't be done remotely.
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