How to change a lock cylinder on a uPVC door in three steps

Close up of cylinder lock on door with key in lock
(Image credit: Getty Images)

How to change a lock cylinder is a handy skill that can potentially save you hundreds of pounds calling out a locksmith — especially if paying for a urgent visit. 

The barrel in a lock cylinder can become damaged or simply wear out and when this happens the lock can become difficult to operate. Alternatively, you might want to change the locks for security reasons. If you are moving house, it can be a prudent to change the locks as it is impossible to know who might have been given keys prior to you taking ownership or living in it as a rental property.

Here we tell you how to remove the old lock in a uPVC door as well as how to choose the right size lock cylinder to replace it and how to change the lock cylinder. 

How to change a lock cylinder: Step-by-step

Removing and replacing a lock cylinder should take you around 30 minutes and the only tool you need is a screwdriver. 

1. Remove the old lock 

Open your door and look at the edge next to the lock cylinder. Here you will see a screw that is roughly in line with the bottom of the lock cylinder. Get a suitable screwdriver and remove the screw and keep somewhere safe.

Typically, it can be one side of the lock cylinder that will fail, so place your key in the side that still lets you move the key. Now gently push the lock cylinder from the other side and wiggle the key left and right. When the cam lines up the cylinder will move. Push through and pull out via the key side.  

Close up of edge of UPVC door lock

A lock cylinder is kept in place by a retaining screw that roughly lines up with the bottom of the cylinder (Image credit: Steven Jenkins)

2. Measure and get replacement 

Once you have removed the cylinder you can measure up and see what size you need. Measure the overall length of the cylinder and note down. Now measure to the centre of the cam (the movable element that sits above the retaining screw hole) and then the other side. 

The cam is often off centre so it's important that you get the right size. As an example, the cylinder in the image below is 80mm in length with a 35mm/45mm split. 

Close up of lock cylinder for UPVC door with key in and tape measure above

You need to measure the overall length of the cylinder as well as the length to the screw hole to ensure you get the right lock (Image credit: Steven Jenkins)

3. Fit new lock 

Unpack your new lock – they typically come with three keys and three screws – and choose the screw that best matches the length of the original screw. You can use the original screw if you want, just make sure that you try it in the new lock before you fit it to make sure the screw thread is the same. 

Put the key in the lock and push the cylinder through where the old cylinder lock was. Push the screw into the same space as the old one, line up with the retaining screw hole and tighten. Job done. 

Are cylinder locks standard size? 

Unfortunately not, so you need to make sure that you get the right size when you purchase a new lock cylinder. The size you need will depend on the thickness of your door. External doors – like a front or back door come with a full cylinder lock, which means it has key holes on both sides of the lock. One will be on the outside and one on the inside.

Sizes commonly range from 60mm to 110mm for a lock cylinder. So first, you need to know the overall size of your lock cylinder. Remove and measure if you can. You will then need to know the position of the cylinder cam. This is the part of the lock that moves to lock a door. Some are placed in the centre, others are off centre. An example is this Smith & Locke Euro Cylinder lock from B&Q. It has a cylinder length of 95mm with a 45mm/50mm split. 

New grey cylinder lock on wooden background

New lock cylinder price start from around £10 from your local hardware store  (Image credit: Steven Jenkins)

How do I remove the lock barrel from a uPVC door without a key? 

If your lock cylinder has failed and you cannot get a key in either side to move the cam you will need to snap the lock to remove it. First unscrew the door handles on both sides of the door. This will give you access to more of the lock cylinder. 

Now get a pair of mole grips like these Stanley Straight Jaw Locking Plier Mole Grips from B&Q. Place the grips as tightly as possible on the top and bottom of the lock cylinder and push down. Do this a few times until the lock snaps. Now dispose of the lock, fit the new lock and replace the door handles.

How much does it cost to replace a door lock cylinder? 

To call out a locksmith and get them to replace a lock cylinder will cost you around £80. The job should take about 20-30 minutes. But the price can vary depending on how far they have to travel and what brand of lock is used to replace the old one.  

If you are doing the job yourself it will cost you the price of the lock and your time. Locks range anywhere from £10 - £80 depending on material, quality and brand. 

Steve Jenkins

Steve is Homebuilding & Renovating's DIY content editor, and has been a writer and editor for two decades. He is an avid DIYer with over 20 years of experience in transforming and renovating homes. He specialises in painting and decorating, but has strong all-round building skills, having previously worked in the industry for 10 years.