Baffled by this....

The car came with only one remote locking control key, which scyns ok using the method described in the manual (ignition on, press lock twice), but it only works two or three times until it needs syncing again.

New fob batteries and the central locking works perfectly from the driver's door lock. No fault codes logged.

Likely to be the receiver/control unit - or more likely to be the key?

TIA.