Most break-ins through modern doors are not brute force. They are attacks on the cylinder — snapping, bumping or drilling — that take seconds and leave the rest of a perfectly good door untouched. Which means door security is mostly a hardware question, and a fairly cheap one to answer.
This guide covers the faults that stop a door locking properly, the standards worth knowing, and what the upgrades cost.
The faults we get called to most
| Symptom | Cause | Repair | Typical cost |
|---|---|---|---|
| Handle lifts but will not lock | Gearbox failing | Replace multi-point mechanism | £140 – £280 |
| Handle needs forcing upward | Door dropped, hooks catching keeps | Hinge adjustment | £45 – £90 |
| Key turns endlessly | Cylinder cam or gearbox failure | Cylinder or mechanism replacement | £90 – £280 |
| Key stiff, worse in cold | Dry or worn cylinder | Lubricate or replace cylinder | £0 – £120 |
| Handle floppy | Broken spring cassette in handle | New handle set | £60 – £120 |
| Key snapped in the lock | Worn key or misaligned door | Extraction and new cylinder | £90 – £180 |
| Door locks but rattles | Keeps set too loose | Adjust keeps and compression | £45 – £90 |
Cylinder standards worth knowing
The key figure is snap resistance. A three-star TS007 cylinder is designed to resist snapping, bumping, drilling and picking. Alternatively, a one-star cylinder combined with a two-star security handle gives equivalent protection.
Older doors frequently still have a plain euro cylinder with no snap protection, and that is the single cheapest meaningful upgrade available on a uPVC or composite door.
| Upgrade | Cost fitted | Benefit |
|---|---|---|
| 3-star anti-snap euro cylinder | £55 – £110 | Very high — removes the most common attack |
| 2-star security handle set | £70 – £140 | High, protects a one-star cylinder |
| Hinge bolts / dog bolts | £40 – £90 | Moderate, resists hinge-side attack |
| Laminated glass in side panels | £120 – £300 | High where glazing is next to the lock |
| Letterplate cowl or restrictor | £25 – £60 | Moderate, prevents fishing |
| Full multi-point mechanism upgrade | £160 – £300 | High if the current one is roller-only |
| New composite door | £950 – £2,600 | Highest, but rarely necessary for security alone |
Do not force a stiff door
The overwhelming majority of gearbox failures we see are caused by people lifting the handle hard against a door that has dropped a few millimetres. The mechanism is fighting the frame, and eventually the cast component inside gives up.
If the handle does not lift with light pressure, the door needs adjusting, not more force. Adjusting the hinges is cheap; a new mechanism is not.
Locked out or locked in
- If the door will not lock and you have to leave, it is an emergency — a temporary cylinder or mechanism can usually be fitted the same day.
- If the key has snapped in the cylinder, do not try to force the stub out with pliers; that often pushes it deeper.
- If you are locked out, a locksmith can usually pick or snap the cylinder and fit a new one, which is far cheaper than damaging the door.
- Keep a spare key with someone nearby rather than in an outside keysafe with a weak code.
What insurers expect
Most home insurance policies expect final exit doors to be locked with a key when the property is unoccupied. On a uPVC door that means lifting the handle and turning the key, not merely pulling the door shut.
Check your own policy wording for lock specification requirements, particularly on side and back doors, before assuming you are covered.
Getting it sorted
Lock work is quick and cheap compared with door replacement, and it is almost always the right first step. We carry common cylinders and multi-point gearboxes across Central Scotland and can usually get a door secure on the first visit.
Common questions
Yes, if you measure the cylinder correctly from the fixing screw to each face. Get it wrong and it will either protrude — which is a snapping risk — or not reach.
Want a straight answer on your own windows or doors?
DM Installations fits and repairs windows and doors across Central Scotland — Cumbernauld, Glasgow, Falkirk, Stirling and the surrounding towns. Free survey, written quote, and an honest answer on whether you need a repair or a replacement.
Related guides
How to Adjust a uPVC Door
Which screw does what on flag, butt and rebate hinges, and how to get a dropped or sticking door closing properly again.
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Side-by-side on price, security, insulation and lifespan, plus the situations where uPVC is still the better buy.
Cost guidesComposite Front Door Cost
Fitted composite door prices, the extras that add up, and how to tell a well-specified door from a cheap one.