Why frost makes locks stiff
A uPVC door lock is really two systems working together: the euro cylinder, which the key turns, and the multipoint gearbox inside the door edge, which pushes hooks and bolts out into the frame keeps. Both have moving metal parts sitting in a small amount of lubricant.
In cold weather that lubricant thickens, especially if it is an old grease-based product or simply years of dust and grime that has never been cleaned out. The metal itself also contracts slightly, tightening tolerances that were already snug. On top of that, the uPVC frame and the rubber gasket around the door both stiffen and shrink a little in frost, so the door sits fractionally tighter in its frame and needs more effort to pull shut before the lock can engage at all.
None of that means anything is broken. It usually just means the lock is having to work harder to do the same job it managed easily in summer.
Lubrication that helps versus lubrication that harms
This is where most stiff locks either get fixed in two minutes or made worse. Household oils such as WD40, olive oil or 3-in-1 oil are the wrong choice for a euro cylinder. They are wet lubricants that attract dust and grit, which then get worked deep into the pins by the key, and within a season the lock is stickier than before.
The correct product is a dry PTFE-based spray or lock lubricant, sold cheaply at most hardware shops. It is designed to coat the pins without collecting debris.
- Spray dry PTFE lubricant into the keyway itself, not just around the outside of the cylinder
- Insert and turn the key several times to work the lubricant through the pins
- Wipe away any excess so it does not run down the door face
- For the gearbox, a light spray along the visible edge mechanism while the door is open can help, but do not force it
- Avoid oil, grease, graphite powder or petroleum jelly in a cylinder
Key turns but the door will not lock
If the key rotates smoothly but the hooks, rollers or bolts do not fully extend, lubricant is not the fix. This points to the gearbox rather than the cylinder, and often to the door having dropped slightly on its hinges so the keeps and the locking points no longer line up.
Try lifting the door handle firmly upward before turning the key, since this is what actually drives the gearbox. If that changes nothing and the door has felt increasingly reluctant to lock over several weeks rather than appearing suddenly with the cold snap, the gearbox mechanism is likely wearing out and cold weather has just tipped it over the edge.
Get a stiff lock checked properly
If lubricant has not solved it, or the door will not lock at all, get in touch and we will take a look and sort a cylinder or gearbox as needed.
When the cylinder itself is failing
A cylinder that is stiff every single day regardless of temperature, that needs the door slammed to turn, or where the key sticks halfway and will not come back out, has usually gone beyond lubrication. Pins wear, springs weaken, and eventually spraying more product in just delays a full failure, often at the worst possible moment such as leaving for work.
Cylinders are a cheap, quick swap and it is worth upgrading to a TS007 3-star rated cylinder while it is out, since this also improves resistance to snapping and picking, matching the wider security standards this site already sets out.
Frozen or just stiff?
A truly frozen lock is rare on a sheltered door and usually follows rain getting into the cylinder then freezing overnight. More often the lock is simply stiff because lubricant has thickened. Warming the key slightly and using a dry lubricant is safer than forcing it, which can snap the key or damage the cylinder.
Preventing it next winter
A little maintenance before the cold months helps:
- Use a dry PTFE lubricant in the cylinder, not oil or grease
- Lightly oil the locking points along the door edge
- Check hinge adjustment so the door closes without pushing