Updated November 2026. Written by the Watchdog Locksmiths team in Greenford, West London. Our locksmiths are DBS-checked and our work carries a 12-month guarantee on parts and labour.
Key takeaways
- French doors and sliding patio doors use different locks: French doors usually have a multipoint lock with a euro cylinder, sliding doors use a hook lock.
- A stiff handle or a key that will not turn is usually a sagging door, a dirty track or a worn mechanism, and it is better fixed before it fails.
- Patio doors are a favourite entry point, so check the cylinder is anti-snap and that sliding doors cannot be lifted off their track.
- Do not fit a lock that stops you opening the door quickly from inside: patio doors are often an escape route.
Patio doors and French doors give us light and garden access, but they are also large glass openings at the back of the house, often out of sight. When the lock sticks or the key is lost, it is more than an annoyance. This guide covers the common faults and how to keep these doors secure.
French doors and sliding patio doors: what locks do they have?
- French doors (hinged pair). The main door usually has a multipoint lock with a lever handle and euro cylinder, much like a uPVC front door. The second door is held by bolts at the top and bottom.
- Sliding patio doors. A hook lock on the moving leaf engages with a keep in the frame, and is often operated with a lever handle and a cylinder.
Common patio and French door problems
| Problem | Likely cause | What helps |
|---|---|---|
| Key will not turn | Worn cylinder, door out of line, mechanism seized | Check alignment and lubricate; replace the cylinder if worn |
| Handle stiff or will not lift | Sagging door, dirty or dry mechanism, failing gearbox | Adjust hinges, clean the mechanism, repair the gearbox |
| Door will not slide smoothly | Dirty track, worn rollers | Clean the track and replace worn rollers |
| Door will not lock fully | Misaligned keeps, worn hook lock | Adjust or replace the keeps and hook |
| Lost keys | Keys misplaced or stolen | Replace the cylinder so old keys stop working |
Many of these faults are the same ones we see on uPVC front doors. Our uPVC door lock problems guide covers the safe checks you can try. If the door is aluminium or a branded system such as Schüco, the mechanism is often a particular type, so send us a photo on WhatsApp before we attend.
How to make patio doors harder to break into
- Fit a 3-star anti-snap cylinder. A standard cylinder can be snapped. See how snapping works.
- Check the sliding door cannot be lifted out of its track. Anti-lift devices and extra locks can help on older sliders.
- Add a second lock if your insurer asks for one. Always confirm what your policy needs. See 3-star locks and insurance.
- Keep the door usable as an exit. A thumb-turn cylinder on the inside lets everyone leave without a key.
What it costs
Our 2026 price list shows door opening on a failed mechanism at £69.99, a replacement gearbox mechanism from £129.99 and a full mechanism from £249.99. A high-security 3-star cylinder starts from £89.99 fitted. See the price list and our price guide.
Frequently asked questions
Why won’t my French door key turn?
The most likely causes are a door that has dropped and is catching on the frame, a worn cylinder or a mechanism that needs lubricating. Do not force the key. If it still will not turn, call a locksmith.
Can you fit a lock on a sliding patio door?
Yes. Options include a replacement hook lock, an additional lock and anti-lift protection. The best choice depends on the door system.
I have lost the keys to my patio door. What do I do?
Have the cylinder replaced so the lost keys no longer work. Read what you need after losing keys.
Can you open a locked patio door without damage?
Often yes. We try non-destructive entry first. If the door must be drilled to open, we tell you before we start.
Patio or French door lock giving trouble?
Contact Watchdog Locksmiths or send us a photo on WhatsApp and we will give you a clear quote before any work starts.
