Overview
'It's fine for a week then it sticks again' is a classic sign of either a worn gearbox that only fails under load, or seasonal movement in the door. The permanent fix is nearly always alignment plus new gearbox.
Symptoms
- Locks fine some days, sticky others.
- Worse when it's very hot or very cold.
- Getting steadily worse over months.
- Occasional need to slam the door to lock it.
Common causes
- Gearbox pawl worn - engages inconsistently.
- Seasonal expansion moving the door in and out of alignment.
- Hinges loosening under repeated stress.
- Cylinder cam wear.
When to call a professional
- The pattern is getting worse.
- You've had to slam it more than once.
- It's failed to lock at all on any occasion.
Prevention
- Lubricate the cylinder twice a year with a graphite or PTFE lock spray - never WD-40 or oil.
- Grease the hooks and rollers on the door edge every 6 months.
- Always lift the handle to engage the multi-point locks before turning the key - this takes load off the gearbox.
- Never force a stiff key - book a service call before the mechanism snaps.