Quick answer
A lock that sticks intermittently — fine for days, then sticky again — points to a gearbox pawl wearing unevenly or a door moving in and out of tolerance with the seasons. Logging when it sticks against the weather is the fastest way to diagnose it. Left alone it typically worsens until it fails completely.
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.
Why intermittent faults are harder to trust than constant ones
A lock that's stiff every single time is at least predictable — you know to expect it and plan accordingly. A lock that works perfectly nine days out of ten and then sticks on the tenth is more dangerous precisely because it breeds false confidence, and the day it fails is rarely a convenient one.
This pattern is also genuinely harder to diagnose over the phone, which is why we always ask customers to note down roughly when the sticking happens — time of day, whether it followed a spell of hot or cold weather, whether it's worse after rain.
Seasonal expansion — Cornwall's particular version of this problem
Composite door slabs, like any manufactured material, expand and contract slightly with temperature, and Cornwall's swings between a mild, damp winter and a hot, dry August can be more pronounced at the coast than the average UK inland figure suggests, particularly on south and west-facing doors that see direct sun for much of the day.
A door sitting right on the edge of correct alignment might close and lock perfectly on a cool, damp morning and then bind by mid-afternoon once the slab has warmed and expanded by a millimetre or two — enough to change how cleanly a hook drops into its keep.
Mechanical wear that only shows up under load
A gearbox pawl — the small component that holds the mechanism in its locked position — can wear unevenly, engaging correctly most of the time but slipping or catching under particular conditions, such as when the door is pulled slightly out of square by wind pressure at the moment of locking.
This kind of wear tends to worsen gradually and rarely fixes itself; if you've noticed the sticking becoming more frequent over a period of weeks or months, that trajectory alone is worth acting on rather than waiting for a pattern to fully emerge.
- Log the date, time and weather each time it sticks
- Note if it happens more after wind, rain or direct sun exposure
- Check hinge screws remain tight — loosening compounds seasonal movement
- Track whether the frequency is increasing month to month
When 'just lubricate it' stops being the answer
Lubrication genuinely helps in the early stages, and a proper graphite or PTFE application can extend the life of a marginal mechanism by months or occasionally a couple of years. But lubricant cannot compensate for a hook that's genuinely misaligned by several millimetres, or a pawl that has worn past its tolerance.
If you've already tried lubricating the cylinder and the sticking pattern hasn't changed at all, that's a reasonably strong indicator the fault is mechanical or alignment-based rather than a lubrication issue, and a service visit is the more useful next step.
The 'had to slam it to lock' warning sign
If you've ever needed to slam the door harder than normal to get it to lock, take that seriously — it means the door was out of position enough that only extra force compensated, and that force is itself accelerating wear on the hooks and keeps. Each slam makes the next lock cycle marginally more likely to stick again.
We'd always rather see a customer after the first occasion this happens than after the fifth, because the repair required is often identical but considerably cheaper when caught early — a straightforward hinge and keep adjustment rather than a full mechanism replacement.
What a permanent fix actually looks like
A proper resolution usually combines two things: correcting the underlying alignment so the door sits square in the frame across a realistic range of temperatures, and replacing any gearbox component that's already showing wear rather than waiting for it to fail outright.
Done properly, this combination typically buys several years of trouble-free locking, whereas repeated lubrication alone without addressing alignment tends to only delay the same fault by a few months at a time.
What we look for that homeowners usually miss
Recurring sticking is rarely random, even when it feels that way. On a visit we'll check the exact conditions the customer reports it under — time of day, weather, whether it's worse after rain — because a pattern tied to humidity points to timber swell in the frame, while a pattern tied to temperature alone points to the composite skin itself expanding.
We also check whether the sticking point is always in the same place on the door's travel, which tells us whether we're dealing with one high spot (a single misaligned hinge or keep) versus a more general tightness across the whole opening.
Why 'it comes and goes' is the hardest pattern to fix badly
A lock that sticks constantly is, oddly, easier to diagnose than one that comes and goes, because intermittent faults are usually sitting right on a threshold — a door that's a millimetre from binding on a humid day but fine on a dry one. Fixing this properly means adjusting past the threshold with enough margin that ordinary seasonal swings don't bring it back.
A rushed fix that only addresses today's conditions often reappears within a few months once the weather shifts, which is why we always ask what the conditions were on the worst occurrences, not just the day of the visit.
Seasonal movement across a Cornish year
Cornwall's mild but consistently damp climate means composite doors here see less dramatic temperature swings than doors further inland or further north, but considerably more moisture cycling. That means the sticking we see tends to be driven more by frame moisture content than by thermal expansion of the door slab itself.
This is worth knowing because a fix aimed purely at heat expansion — trimming or planing, for instance — can miss the real cause entirely on a Cornish property, whereas addressing drainage and frame sealing often resolves sticking that looks identical to a thermal issue.
What ongoing sticking does to the mechanism over time
Every time a door has to be shoved or leaned into to get the lock to engage, that extra force transfers through the hooks and gearbox rather than being absorbed anywhere else. Repeated over months, this accelerates gearbox wear in a mechanism that would otherwise have had years of life left.
We regularly find gearboxes that have failed years earlier than expected purely because the door had a persistent sticking issue that was never addressed, with the lock simply forced through it on every use.
What to check yourself before booking a visit
Run your hand around the full perimeter of the door while it's closed, feeling for spots where the seal is compressed unevenly or where the door visibly touches the frame off-centre. Note which corner feels tightest — top hinge side, bottom hinge side, or the lock side — as this single observation often points straight to which hinge needs adjusting.
Typical repair costs in Cornwall
| Work | Typical price | Notes |
|---|---|---|
| Diagnostic visit with lubrication and adjustment | £75-£120 | Resolves the majority of early-stage cases |
| Hinge realignment for seasonal movement | £90-£140 | Addresses root cause rather than symptom |
| Gearbox replacement | £200-£300 | Where wear has progressed too far for adjustment alone |
| Combined service (hinges + gearbox + cylinder) | £250-£360 | Best value if multiple components are aging together |
Guide prices only — we confirm the cost after seeing the door.
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.
