Open the door and check the metal faceplate. Measure the PZ (centre of the handle spindle to centre of the keyhole, usually 92mm) and the backset (edge of the faceplate to centre of the keyhole, usually 35mm or 45mm), find the brand stamped on the faceplate, and note the locking points.
If the handle is floppy or the key turns but nothing moves, it's usually just the gearbox, which you can replace on its own for much less than a full lock.
Most uPVC and composite doors have a multipoint lock: a long metal strip in the edge of the door with a gearbox in the middle and several locking points, such as hooks, rollers or bolts, above and below it. There are hundreds of versions, but you can identify yours with a tape measure, a quick look at the faceplate and the steps below.
Before you buy a whole new lock, check whether you only need the gearbox. It’s the part that fails most often, and it costs a fraction of a full lock.
Open the door, lift the handle and turn the key, and watch the locking points along the edge of the door.
Take the measurements with the door open, on the metal faceplate in the edge of the door.
The PZ and backset are the two measurements you need for a gearbox. For a full lock you also need the faceplate width and the locking points.
Know your PZ and backset?
Find your replacement gearbox. Most fit your existing lock strip and both left and right-handed doors.
Look along the faceplate for a name or logo stamped into the metal. You may need to open the door fully and look closely, as it can be worn or painted over. Common brands include Winkhaus, GU (Ferco), ERA, Fullex, Maco, Roto, Yale, Lockmaster, Mila, Avocet and Fuhr.
The brand matters most if you’re replacing the gearbox only, because a gearbox has to match the strip it fits onto. If you can’t find a name, a photo of the gearbox and faceplate is usually enough for us to identify it.
Lift the handle with the door open so all the locking points stick out. Note what type each one is and how many there are.
For a full lock, you also need the distance from the centre of the handle spindle to each locking point, and the overall length of the strip.
A single spindle lock has one square bar through both handles, so the door opens with either handle. A split spindle lock lets the outside handle lift to lock the door but not open it, so you need a key to get in from outside. Your new gearbox or lock must match. Our guide to single and split spindle locks explains how to tell them apart.
The gearbox is the most common part of a multipoint lock to fail, and replacing it is much cheaper than buying a full lock. To find the right one, you need the brand, the PZ, the backset and whether it’s single or split spindle. Our most popular gearboxes are:
Most gearboxes fit both left and right-handed doors and reuse your existing strip. For fitting help, see our guide on how to replace a uPVC multipoint door lock, or browse all our replacement gearboxes.
Our best-selling gearbox
GU Old Type, 35mm backset, 92mm PZ, single spindle. £14.99.
We supply full multipoint locks from our trade counter in Aintree, Liverpool, including the Winkhaus Cobra, Winkhaus Thunderbolt and Roto locks we fit most often. Because there are so many versions, we’ll check you’re getting the right one before you buy.
Email a photo of the full length of your lock, plus a close-up of the gearbox and faceplate, to info@homesecureshop.co.uk. Include the PZ, backset and faceplate width if you can. We’ll identify it and let you know the price and availability. You can also call us on 0151 521 8089, or bring your old lock to the counter.
If you’re replacing the lock or gearbox, it’s a good time to check the euro cylinder too. A standard cylinder can be snapped in seconds. A TS007 3-star anti-snap cylinder protects the whole locking system, not just the mechanism. Our guide on how to measure a euro cylinder shows you how to get the right size.
Upgrade the cylinder while you're at it
Avocet ABS, TS007 3-star anti-snap, in every size from 30 × 30mm to 60 × 60mm. £44.99.
