[HowTo] Retune TVHeadend DVB for UK Freeview digital switchover

So yesterday my local TV transmitter moved one mux to a different frequency as part of the ‘700MHz clearance’ programme. In theory, if you have Network Discovery turned on for your network, and ‘Idle scan’ turned on for your tuner TVHeadend should automatically update and find the new transmissions. That didn’t happen for me. Here’s what to do:

Step 1: re-tune your TV, watching closely and noting down which channels it picks up. In my case, channel 35 was new and channel 55 had gone.

Step 2: find out what frequencies those channels correspond to, eg 35 is 586MHz and 55 is 746MHz. ukfree.tv is a useful resource but its information about the 2018 switchover is not up to date. https://www.a516digital.com/ seems to be better maintained (thanks to @ac16161 for that spot).

Step 3: In the TVH webui, go to Configuration->DVB Inputs->Muxes, select a mux with the frequency no longer being used and click edit. Just change the frequency (it’s in Hz!):

If you have set the view level to Advanced, you can also set the Scan status to ACTIVE to force a scan.

Click Save and you should get OK in the Scan result column in a while.

If a number of muxes are changing at the same time, make sure you identify HD muxes as they have different settings. They should look like this: