So, new TV, empty space in bedroom, TV point and Ethernet points nearby, all I had to do was finish the wiring (left unconnected as it was not needed 15 years ago!) and scan for channels. Simple.
OK. So I had a splitter and then found a smaller one so used that. Stuck it to the wall in the airing cupboard, wired in the CT125 coming down from the loft and two TV coax runs to the two bedrooms, and connected the other end of the CT125 to the aerial distribution amp in the wiring closet. Turned the TV on and it began scanning. And found very little. Hmmm. Well, it found the HD channels but would not receive them.
Out with the meter. Connectivity fine from the splitter to the TV, so blamed the splitter and wired in the larger one. Rescanned. Same thing. Got a barrel connector and bypassed the splitter. No difference. Went to the wiring closet and checked the connection there… which I had plugged into the DAB aerial feed input, rather than a TV output!
Put the smaller splitter back in and fitted the cables again and all is well.