Tvheadend

Do not remove old channels,
just scan and map with merge existing.

I am assuming you have Freeview? Why would you use 'custom channel numbers'? Channel numbers are standardised across Freeview everywhere AFAIK, so using the standard numbers would mean everything just stayed in step. Plus mean you could look them up in those publications that use channel numbers.

Scan and map and merge existing sounds like what I need to do, I'll give that a next time I move.

I change the channel numbers so things are sensibly organised in the guide on Kodi, eg itv next to itv+1 etc.

So I've tried this now and it doesn't work. I think somewhere along the line the existing mappings got messed up and the channel names all became {name-not-set}, so I'm not able to merge existing. Any idea why this might have happened and how I can prevent it?

With version of TVH you use?
what are setting of "map channel" used?

Josh Short wrote:

So I've tried this now and it doesn't work.

Short explanation - assume:

first network (e.g. DVB-T Wales ) --> has "Services" e.g. BBC 1 --> may become a channel "BBC1"

second network (e.g. SAT on boat) --> has "Services" e.g. BBC 1 --> may become a channel "BBC1_SAT"
OR --> may be merged to first channel "BBC 1"

Now you have a channel with different services. Which service shall be used when a channel is requested ?

Right: tvh uses the first one in the list IF there is no priority set. So you will see on every
channel the service wich was first added. But this service is "upstream" / unavailable.

Even if merging works you will NOT see only active services if you choose a channel. You have to
finetune the prio of the services within the channel. Or you have to wait until tvh discovers that
the service is unavailable. If there are 5 services it takes ~~25 sec until tvh reaches the active
service. (BTW: Often tvh simply doesn't switch : dunno.)

The whole concept of "merging" suits better for different static sources (which may have a different prio.)
StreamHandover and takeover sometimes work - but often it doesn't.

Any idea why this might have happened and how I can prevent it?

First and biggest mistake was listening to saen acro. It's a little bit more complicated.