Usually this is an authorisation issue in boxes that have been disconnected for a while. You can either ring customers services to have a "hit" sent to the box, or if prepared to wait, the Forum Team here can do it.
Cable customer since 1993. Services: FH TV, Sky Sports & Movies (2xV+), Talk Unlim Telco, VIVID 100, Virgin PAYG Mobile
Firstly I'd like to welcome you to the forums and say that I'm sorry to hear that you're getting the error code ap52 on your second set top box.
I've run some testing on the account and can see that your second set top box is showing that it is unable to gain a signal. So I'd have to ask you firstly if you are able to again check the wires, also check the length of the wire, as building work has been done, just to make sure there are no breaks in the cable feeding the set top box.
The next step would be to book a technician to call out and investigate further for you, I've sent you a private message in order to set the wheels in motion, please look to the top left of this page where you'll see a red envelope icon, click on that and you'll see my message.