central locking problem

[Kcboiye]

latley ive been having issues with my central locking, when i go to lock it, itll lock but then unlock straight away and possibly set the alarm off when i open the door, but also, when i put the new door on, the lock tab on the inside wont go down all the way, its clipped on properly but it wont go down wen i lock it

any ideas on what might be issue(s)?

 

[The1]

locking mech in the door is jamed, it usually beeps if it doesn't lock a door properly but yes the alarm will still be activated.

 

[Kcboiye]

im gonna try and replace the locking motor from the original door and see wat that does