Polo central door locking problems

Hi All,

I have 54 Polo GT TDI with remote central locking and deadlocks. 

So following on from a previous problem (last year)  with my central locking where the front passenger door wouldn’t unlock, I have an update and a further question.

The door randomly unlocked itself, I then seized the opportunity and fitted a new lock, non OEM. Then, after a good few months, the lock again failed to unlock and despite trying and trying, it was back to square one. I thought how can this bed? What are the chances of that happening? I then wondered if it might be something else, like a separate control unit, so I looked in my Haynes manual and it says that the central locking is controlled by a multi-function control unit, which also controls amongst other things, the alarm. Well strangely I have also had problems with the alarm going off for no reason. This all seems to point to the multi-function control unit.

So, my questions is, can both locking problems actually be attributed to this multi-function control unit and how would I go about testing it?  Is it something I can do with a meter or does it require a specialist equipment?

Many thanks for your time.