French, Patio & Bifold Door Locks: Faults, Repairs & Security Guidance

Max the Locksmith · July 2026

The short answer: garden doors fail by type — French pairs go out of line and jam their shootbolts, sliding patios wear their hook latches and rollers, bifolds drop on their carriages until hooks and drop-bolts stop meeting. All of it is parts-and-adjustment work at the flat £85 labour + parts (+ VAT), and because these are the doors burglars test first, a garden door that “mostly locks” deserves fixing this week, not this year. Common mechanisms are stocked in the van — price guide.

French doors: two leaves, one system, one classic fault

A French pair locks as a chain: the slave leaf anchors itself to frame and threshold with shootbolts, then the master leaf locks into the slave with a multipoint mechanism. The chain’s weak link is movement — garden doors live in weather and sun, and when either leaf drops or the slave’s shootbolts stop seating, the master’s hooks miss, the handle gets forced, and the gearbox strips on schedule.

Troubleshoot in this order. Lock the slave leaf alone: do the shootbolts throw crisply into their keeps, top and bottom? (The bottom one fails first — grit and swelling.) Then close the master and watch where its hooks land against the slave. Only locks when you knee-lift one leaf = alignment, often no parts at all. Slave bolts won’t throw = shootbolt or keep fault. Master handle stiff even with both doors open = the gearbox itself. And if the pair jams shut entirely — don’t crowbar the meeting stile; it destroys both leaves’ seals. Max opens them without damage first, then fixes the cause.

Sliding patio doors: hooks, rollers and the lift test

Sliders lock with hook latches into a frame keep, and ride on rollers that quietly determine everything. Two faults dominate. The hook lock wears — key turns without a solid clunk, or the hooks won’t release. And the rollers wear flat — the door gets heavier to slide each year and sits lower, until the hooks miss the keep. The lift test: if gently lifting the slider while locking makes it catch, your rollers are done. Roller replacement plus track cleaning transforms a door people have wrestled for a decade — “we thought it just was like that” is the standard reaction. A slider that bumps and grinds along the track is also chewing its own track rail; sooner is cheaper.

Patio security has one extra rule: a slider must be protected against being lifted off its track — the classic attack. Anti-lift blocks or a patio lock bar close it for a few pounds in parts; fitting them is a five-minute add-on to any repair, and part of the wider list in additional security.

Bifold doors: locks and hinges are the same conversation

Bifolds combine everything above: a multipoint on the lead door, drop-bolts and finger-pull latches on the intermediate leaves, hinges between every panel and top or bottom carriages doing the rolling. When a bifold gets hard to lock, the sequence to check is carriage → hinges → alignment → then lock, because a dropped carriage misaligns every panel behind it — the lock is usually the victim, not the culprit. Signs your bifold’s running gear is going: panels that need a shove to meet, drop-bolts that no longer find their floor sockets, and the grey grinding streaks around hinge knuckles that mean a hinge is wearing internally. Carriages, hinge sets, drop-bolts and gearboxes are all serviceable; sticky bifolds rarely need panels or glass.

The security honest-talk (all three types)

Garden doors are a favourite way in — glazed, at the back, out of sight from Sherwood to West Bridgford. What genuinely helps: anti-snap cylinders wherever a euro cylinder drives the mechanism (why, which rating); shootbolts and drop-bolts that actually engage (this whole post); anti-lift on sliders; and using the deadlock every night — an unlifted handle on a multipoint is barely locked at all, the same point made in how to make a uPVC door more secure. What doesn’t help: a stick in the slider track as your only measure, and security theatre bought before basic engagement is fixed. After any attempt or break-in, secure-then-upgrade is the order of operations.

Parts stock, and the overnight rule

French shootbolt kits, patio hook cases, rollers, drop-bolts, gearboxes and cylinders in the common patterns (Fuhr, GU, Maco, ERA and equivalents) travel in the van — most garden-door repairs are one visit. Obsolete slider mechanisms and some bifold carriages occasionally need sourcing; when that’s yours, the door is left closing, locking and secure the same day — temporary keeps or a secured leaf where needed — and finished when the part lands, usually next morning. Never an unlockable back door overnight.

What it costs (on average)

The main issues — alignment, shootbolts, hook cases, rollers, drop-bolts — resolve at the flat £85 + parts (+ VAT); adjustment-only French visits are often just the £85. On average: French gearbox or shootbolt kits £30–£220, patio hook cases £40–£150, roller pairs £20–£80, bifold drop-bolts and latches £15–£60, anti-lift additions £15–£60. The honest caveat: bifold carriage sets and some obsolete slider mechanisms can run £250–£500+ — rare, flagged first, exact figure before work starts. And if a bifold job grows beyond one pair of hands — a full panel-train rebuild, a multi-door refit — no problem: Max has a team for the bigger works, priced strictly by complexity and quoted as a fixed figure up front. Price guide.

Quick answers

My French doors only lock if I slam or lift one door — what’s wrong?

The slave leaf’s shootbolts are missing their keeps because a leaf has dropped. Alignment cures it; ignored, it strips the master gearbox and doubles the job.

My sliding patio door has become really heavy to slide — is that the lock?

It’s the rollers. Worn rollers drop the door so the hooks miss the keep — replacement plus track cleaning restores both the glide and the lock.

Our bifold won’t lock unless we shove the panels together — lock fault?

Usually a dropped carriage or worn hinges misaligning the panel train — the lock is the last domino. Check for grinding marks at the hinges and shoved-to-meet panels; the hinge failure guide covers the signs.

Are French doors easy to break into?

A well-adjusted French pair with engaged shootbolts and an anti-snap cylinder is solid. The vulnerable ones are simply out of alignment — half-locked without their owners knowing. That’s an £85 fix, not a new-doors problem.

Can you repair garden door locks the same day?

Usually — the common mechanisms are in the van, and anything rarer gets made secure the same day with the part fitted next morning. Same-day cover runs across Nottingham, Derby and Mansfield.

Is a bar or stick in the patio track enough security?

As the only measure, no — it does nothing against lifting the door off its track, which is the actual attack. Anti-lift blocks plus a healthy hook lock is the proper pairing.

Sorted? What most readers check next

• Door repairs — all door types
• Door Hinge Failure Signs — uPVC, composite, wooden & bifold
• uPVC Door Gearbox Replacement
• Are anti-snap locks worth it?
• Additional security upgrades

Garden doors misbehaving? Call 07552 421433 or WhatsApp a photo — £85 + parts (+ VAT), no call-out fee, same-day across Nottingham.