How to Fit & Replace Door Locks

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When moving into a new house, changing the door locks is an excellent way to ensure your property is completely secure. If all other methods of door lock repair have failed, it's definitely time for a total door lock replacement.

Whether you need to fix a bathroom door lock, upgrade your patio door lock, or figure out how to repair door lock issues on an exterior entrance, this straightforward guide has you covered. Let's explore the different options and get your home secured.

A Euro profile cylinder lock is the best option for a uPVC door lock or composite doors, while a mortice sash lock works perfectly for wooden internal doors.
To change a mortice sash lock, you need to remove the faceplate and handle, extract the old lock body using pliers, and slide the replacement firmly into the existing mortice hole.
You must always wear safety goggles when drilling and ensure your replacement exterior locks are certified to BS3621 or display the Kitemark symbol for maximum home security.

Tools and Materials

Understanding different door lock types

Before learning how to replace a door lock, you’ll need to identify what you already have. Here’s a summary of the main types of lock and the door materials they are best suited for:

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Also known as bolt-through latches, these are commonly found on internal doors, like a bathroom door lock or a bedroom door handle. They require a mortice, or hole, to be carved into the door edge. They are best suited for solid wooden doors.

Commonly used for front door locks, these offer excellent security. If you need a uPVC door lock or a composite door lock, this is usually the type you have. They’re also very easy to change, as you don't need to remove the whole mechanism to fix or replace them.

This lock is attached directly to the door's surface. It's ideal for thinner doors where you cannot drill a deep mortice hole. They are commonly found on wooden external doors and are sometimes paired with a separate nightlatch.

Preparing for your door lock replacement

When choosing replacement locks, it's best to look for BS3621 or Kitemarked products. In fact, many home insurers insist on this.

For a mortice lock, measure the distance from the door edge to the centre of the keyhole. If it's 45mm, you need a 64mm lock. If it's 57mm, grab a 76mm lock.

For a Euro profile lock, measure from the centre fixing screw to the outside of the lock on both sides. If your old Euro lock sticks out more than 5mm beyond the faceplate, it is vulnerable to a 'snap attack'. Always choose a flush replacement.

Top tip: Remember to wear safety goggles when drilling or using a chisel and always carve away from your body. Doors can be heavy, so ask for help if you are taking one off its hinges.

How to change a mortice sash lock

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With your door open, turn the key so the bolt is locked. Take the key out, then remove the screws holding the faceplate, internal door handle, and spindle bar. Keep these safe for later.

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Grip the extended bolt using a pair of pliers and firmly pull out the old lock body.

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Compare the components of a door lock you've just removed with your new one. If the new lock body is larger, use a hammer and wood chisel to carefully enlarge the mortice hole until the new lock fits perfectly.

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Once the lock body sits flush, screw the faceplate into position. Replace your spindle bar and door handle. Check that the new key turns smoothly.

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Remove the old strike plate from the door frame. Hold your new one in position to check the fit.

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Chisel away any excess wood if needed, then secure the new strike plate with the supplied screws. Close the door to check everything aligns.

How to change a euro profile cylinder lock

Open the door and locate the central lock fixing screw on the door edge. Unscrew and remove it. Slightly loosen the door handles to help ease the cylinder out.

Put your key in the lock and gently pull it towards you as you turn it to either the left (10 o'clock) or right (2 o'clock) position to align the internal cam. The lock will easily slide out.

Slide the new cylinder into the hole and replace the central fixing screw on the door edge. Then, tighten your door handles. Test the key on both sides before shutting the door.

How to change a rim cylinder lock

On the inside of the door, unscrew the main lock body and keep it safely to one side. Then, remove the two screws holding the existing rim cylinder lock.

Push the old cylinder out from the front, making sure you don't move the mounting plate on the inside of the door.

If the tail bar on your new replacement lock is longer than the old one, use a hacksaw to shorten it so they match perfectly.

Push the new cylinder into place from the outside and fix it with the provided screws. Screw the internal lock body back into position and test it with the key.

Adding security door bolts

If you want extra security for a garage door lock, or a wooden back door, fitting security bolts is a great idea.

Select the correct wood drill bit. Use masking tape to mark the bolt's depth directly onto the drill bit so you don't drill too far.

Drill a horizontal hole into the top and bottom of the door's edge to your marked depth.

Slide the bolts in and mark the outline of the endplates. Use your hammer and chisel to create a shallow recess so the endplates sit totally flush with the door edge.

Hold the bolt against the inside face of the door, flush with the edge. Use a carpenter's awl to clearly mark where the keyholes need to go, then drill them out.

Push the bolts in, line up the keyholes, and screw the endplates into position. Finally, fit the strike plates to the door frame using the bolt's bump to mark the exact position.

Lock installation aftercare

Ensure your locks are clean and lubricated to keep them in good working condition. Use suitable lubricants for the material and finish as using the wrong product could cause permanent damage.

Everyday use means handles and faceplates can eventually come loose. Give your doors a quick check every few months and use a screwdriver to gently tighten up any loose fittings.

For keeping your locks clean, steer clear of abrasive chemical cleaners or scouring pads. They can easily strip away the protective finish on your handles and faceplates, which often leads to rust. Instead, simply wipe them down with a soft, damp cloth and dry thoroughly.

We hope that we’ve been able to help you figure out which type of lock you need and how to replace it. If you need to go a bit further with your door repair, take a look at our guide to fixing a broken door handle.

FAQs

A standard mortice door lock includes a lock body that sits inside the door, a faceplate on the door edge, a spindle bar that connects the handles, and a strike plate fitted to the door frame.

If your door lock is completely jammed shut and you cannot open the door to access the fixing screws, you’ll need to call a professional. It's also best to call a registered expert if you have a complex multi-point locking system on a uPVC door that requires specialist realignment.

If a small piece of the key is sticking out, you might be able to carefully grip it with needle-nose pliers and pull it straight out. If the key is snapped flush inside the cylinder, avoid poking it with everyday tools as this pushes the metal further inside. In this case, you’ll need a broken key extractor tool or the help of a locksmith.