Multipoint Gearboxes & Overnight Locks
If the handles are drooping on your front door, or the lift-locking mechanism is becoming faulty or unreliable, you may have a problem with your centre gearbox, but don't worry! You might not have to replace the whole thing!
On multipoint locks, all of the locking points on the metal strip down the door are actioned by the central locking mechanism known as the gearbox. This is where your handles and cylinder are situated on the door, and allows you to control all of these locking bolts or hooks from the one location rather than having to control them all individually.
Whilst this is a fantastically convenient way to effectively lock all the way up the door rather than just at the centre, it does mean the centre gearbox is having to work much harder to mechanically drive and withdraw all those locking points, especially if the door is fitted tightly against the seals (which they often are). Because of this, it may be that you find your handles start to droop, or the gearbox mechanism begins to slip when lifting the handles to engage the lock.
At this point (even just the droopy handles) you know the gearbox is nearing the end of its functional life and either the lock or the gearbox should be replaced immediately. If you take the lock out of the door, you'll be able to see if you are able to remove the gearbox or not - some are riveted onto the locking strip, others are screwed on.
If you can see the gearbox is riveted on, then you cannot replace the gearbox - even if you are capable of stripping these rivets and own a suitable riveting gun to re-fit the gearbox, the manufacturers who choose to rivet the gearbox on, do not offer replacement gearboxes so it would be a case of replacing the full multipoint lock. This may be more expensive than a gearbox, but it's not necessarily a bad thing to be renewing all of the locking points, as old worn locking points could be bad news for a new gearbox anyway!
If you see that the gearbox is screwed on, then there's a good chance you can replace that gearbox. At this point you should inspect the full locking strip for signs of wear, damage, or corrosion. You should also check all of the hooks / bolts / roller cams along the locking strip to identify if they look to be functioning properly. If you think the whole lock is looking tired or there are signs of wear or damage, then you should consider replacing the whole lock. But if everything looks fine except for the gearbox malfunctioning, then chances are you can simply replace the gearbox and save yourself some unnecessary spending.