Central Locking?

I have a Holden Astra. The Central locking system seemed to have stopped working via the key fob. I have seen since then answers in regards to re-synching the fob. However the system itself has a problem. The back doors intermittently won’t lock/unlock. Occasionally the locks are held down by the solenoid, requiring a set of pliers to lift it. I would appreciate any help, thank you