Front door locking mechanism stiff

[Navrig]

We have a timber core, sheet steel sandwich front door with a G-U lock. It looks like it is a G-U uPVC DOOR LOCK 2 Hook.

Intermittently the locking mechanism will not engage properly and when the handle is lifted it stops short of a full lock UNLESS you give it a hefty lift in which case it engages. Once engaged the key locks it no problem.

I haven't been able to determine what causes the intermittent fault - temperature, dampness, use etc.

The problem is that my daughter and my wife cannot give it enough oooomph meaning that they struggle to lock the door.

As it is a timber core there is no adjustment at the hinges.

The hinges look like this one:

http://www.ironmongerydirect.co.uk/Products/Hinges/Door_Hinges/4059/Strong_Steel_Security_Hinge

Is there any adjustment at the locking side? Should it be lubricated?

 

[crank39]

I take it it'll lock ok when the door is open?

The door has obviously moved somehow/somewhere, try taking the keeps off the frame one by one till it works (so long as they are all seperate) and if poss re-fit the offending keep a touch lower, only 2 or 3mm lower though