I have recently moved over to an adjoining county which is run by another health board while attempting to change my address I was told I have to find another surgery, I find the odd as I know several people using surgeries across the border I have been with my present surgery for 42 years.
Some surgeries will keep on out of area patients and some won't. It depends on whether the surgery will do it and whether the commissioning authority of you new address will pay for it.
I'm afraid its probably true. We moved less than two miles across town but were told by our surgery who I'd been with for 20 years that they could no longer keep me on due to a post code change. For me it was great as I got much better healthcare at the new doctors but I hope you can resolve things. Have a word with one of the doctors perhaps?
Doctors have to pay for the 'out of hours' services they use (when a doctor is called out for an urgent home visit in the night, for example).
It's possible that the surgery you're registered with doesn't have an out of hours contract which covers visits to your new address, whereas other surgeries (with different contracts) might not face the same problem.