If you know what you are doing you can work out what is on Zone 1002, test it and work out if something needs replacing or repair.
Does the system work correctly intermittently or has the system not armed correctly since the original service?
If the original visit was a service I can understand the call out charge for the second visit but if this is a reoccuring issue from the second visit, I wouldn't expect another charge.
I have no idea how much you paid to have the system installed but it not as simple as that, you could swap all the controls and there be a fault on the wiring for example. You can have similar issues with any home service, boiler, lecy etc.