Patio, Sliding and French Door Locks Explained

How do sliding patio door locks work?

A sliding door locks with hook bolts that swing out of the edge of the moving panel and catch in keeps on the frame. A handle or thumb turn throws them, and a euro cylinder on the outside locks them. Most modern sliding doors in uPVC or aluminium use this layout, often with two or more hooks. Older aluminium doors may have a single hook lock with a smaller cylinder, and some of those fittings are no longer made. Many households add a secondary lock, such as a key-locking bolt at the foot of the sliding panel, for times when the house is empty.

How do French door locks work?

French doors have two leaves. The master leaf, the one with the handle you use, carries a multipoint lock worked by a euro cylinder, much like a front door. The slave leaf stays closed most of the time and is held by shootbolts at the top and bottom, thrown by a small lever on its edge. The master's locking points close into the slave leaf, so both have to be in good order. If the slave shootbolts are not thrown, the pair is weaker than either leaf looks. Bi-fold doors follow a similar idea, with a lock on the main leaf and bolts on the others.

Which standard should you look for?

For the cylinder, the same grades as a front door: TS 007 3 star, a 1 star cylinder with a 2 star handle, or Sold Secure SS 312 Diamond. For the door as a whole, PAS 24 tests the doorset, meaning frame, glazing, fittings and lock together, and is the baseline for Secured by Design's Police Preferred Specification. A doorset that passed PAS 24 may carry a label in the frame. If a patio or French door is a final exit, insurers usually expect the same lock grade as on the front door, though wording varies.

How do you tell what you have and when it is failing?

Open the door and look at the edge. A row of hooks on a sliding panel, or a strip with hooks and rollers on a French door, tells you the type, and the maker's name is usually on the faceplate. The common faults are a hook that no longer reaches its keep because the door has dropped or the rollers have worn, a gearbox that has failed so the handle turns without throwing anything, and a seized cylinder on a door that is rarely used. A sliding door that drags or jumps on its track strains the lock as well.

What does a repair cost, and when should you call a locksmith?

The sourced guide for these doors is the uPVC mechanism figure: £85 to £300 for a gearbox repair or replacement mechanism (MLA price list; MyJobQuote). A new cylinder is £105 to £175 fitted, or £137 to £150 for an anti-snap grade (MLA price list, MyJobQuote and Checkatrade). Older sliding doors with discontinued locks can cost more, because a matching part has to be found or the door adapted. Call a locksmith if a patio door will not lock, since a ground-floor door left insecure is a common way in, or if the slave leaf of a French door will not stay shut.

Common questions