300tdi central locking problem

Hi all,
I am new to the landy scene, I bought my M reg 1995 300tdi last October.
All has been good so far, however yesterday my central locking just refused to work.
My fob still arms/disarms the alarm, but none of the doors lock, although I can hear a faint clicking as though they are trying to lock.
I can still lock the tailgate, passenger and driver doors with the key. I have checked the fuse and that is ok.
Does anyone have any ideas what the problem could be?

Can u central lock with the key in the drivers door lock.
The problem it may be something simple like the master actuator requiring ajustment on it's mountings in the drivers door or it's faulty and requires replacing.
And :welcome2:to the Forum.

No, the driver door locks but all the others stay open. I can hear something click though as if the central locking is trying to work.