Bob Lucas wrote:

2. Bin your old Sky+ box and purchase a second-hand replacement.
Sky+ receivers are often available on eBay. However, don't pay more than
£65 for a second-hand receiver (the maximum cost of a service call and
replacement receiver from Sky). If you replace your old receiver, you
will need to phone Sky to marry your viewing card to the replacement.


I'm not sure this is necessary any more - for example if you get a new box
and do the "self install" option, you do a "callback" from the installers
menu and then there is an option in sky interactive (press interactive and
select sky active) to have the box do an additional callback to marry the
card to the box.