Whether you've just moved into a new home; had your keys lost or stolen, or simply want to boost your home security, knowing how to change a lock is one of the most useful DIY skills a homeowner can have. This step-by-step guide walks you through everything you need to know - from choosing the right lock to knowing when you need to call in a professional.
Why You Might Need to Change Your Locks
There are plenty of situations that may require you changing your lock. The most common reasons include:
- Moving into a new home. You have no way of knowing how many copies of the previous keys exist. Former owners, estate agents, contractors, and cleaners could all have had access. Our moving home checklist recommends changing your locks as one of the very first tasks after getting the keys to a new property.
- Lost or stolen keys. If your keys have gone missing, it's important to act quickly - especially if they were lost alongside anything that identifies your home address.
- After a break-in or attempted break-in. Damaged locks should be replaced immediately. This is to ensure your safety and prevent further break-ins.
- End of a tenancy. Landlords should always change locks between tenancies to protect new occupants.
- Upgrading your home security. Older locks may no longer meet insurance requirements or modern security standards.
Different Types of Locks
Before you head to the hardware shop, it's worth knowing what type of lock you're dealing with. The three most common types found in UK homes are:
Cylinder locks (Euro cylinder) - the most common type in uPVC and composite doors. The cylinder is the barrel-shaped component that your key turns. These are relatively simple to replace, though it's vital to choose an anti-snap cylinder, as standard cylinders are vulnerable to a technique known as "lock snapping."
Mortice locks - typically found in older wooden doors. These are set into the body of the door and require a separate key. A 5-lever mortice deadlock is the standard required by most home insurance policies.
Nightlatches (Yale locks) - spring-bolt locks found on many front doors, often used in combination with a mortice lock. They lock automatically when the door closes.
Check your existing lock type before purchasing a replacement - and always look for locks that meet British Standard BS3621 or carry the Sold Secure SS312 Diamond accreditation, as these are widely recognised by insurers and recommended by the police.
What You'll Need
For most standard lock changes, you'll need:
- A replacement lock (same type and size as existing, or a suitable upgrade)
- A flat-head and cross-head screwdriver
- A tape measure (to check the backset distance which will be the measurement from the door edge to the centre of the lock)
- A chisel (if adjusting the recessed area for the faceplate)
- A pencil
How to Change a Euro Cylinder Lock
Swapping a euro cylinder is one of the simpler lock changes a homeowner can do easily.
Step 1: Measure your existing cylinder. Open the door and measure the total length of the cylinder, as well as the distance from the centre fixing screw to each end. This measurement is typically written as, for example, 35/45 (35mm on the outside, 45mm on the inside). You need to buy a replacement that matches these dimensions.
Step 2: Remove the door handle plate (if applicable). Unscrew the screws on the interior door handle plate. Keep them safe as you'll need them later.
Step 3: Open the door and find the fixing screw. Look along the edge of the door for a small screw in the faceplate (the metal plate on the door edge). This is the cylinder retaining screw. Loosen it a few turns, you don't need to remove it fully.
Step 4: Turn the key slightly and pull. Insert your key into the cylinder and turn it slightly so the cam (the metal tab at the back of the cylinder) aligns horizontally. This allows the cylinder to slide out. Pull the cylinder straight out of the door.
Step 5: Insert the new cylinder. Slide the new cylinder into the lock body, ensuring the cam is in the correct position. Turn the key to check it operates the lock smoothly.
Step 6: Tighten the retaining screw. Once the cylinder is correctly seated and operates as expected, tighten the fixing screw in the door edge and reattach the door handle plate.
Step 7: Test thoroughly. Test the lock multiple times from both inside and outside before closing the door. Always have a spare key to hand, just in case!
How to Change a Mortice Lock
Mortice locks are a bit trickier but still manageable for a confident DIYer.
Step 1: Unscrew and remove the door handles and rose plates on both sides of the door.
Step 2: Remove the faceplate screws on the door edge and pull the lock body out of the mortice pocket (the slot cut into the door).
Step 3: Take the old lock to the hardware shop with you if possible, so you can match the size exactly, particularly the case size (height and width) and backset.
Step 4: Slot in the new lock body. It should fit snugly into the mortice pocket. If the faceplate doesn't sit flush, you may need to pare down the recess slightly with a chisel.
Step 5: Reattach the faceplate, handles, and rose plates. Ensure all screws are tightened and both handles move freely.
Step 6: Test with the door open first, then closed. The bolt should extend and retract smoothly and the door should lock and unlock easily from both sides.
Rekeying vs Replacing Locks
If your lock is in good condition but you simply want to ensure old keys no longer work, rekeying is an alternative to a full replacement. This involves changing the internal pin configuration of the lock cylinder so that the old keys no longer operate it. It's a job almost always done by a professional locksmith, but it can be a practical and efficient option in some circumstances, particularly if the lock itself is relatively new and in good working condition.
When to Call a Locksmith
Knowing your limits is just as important as knowing your DIY. There are times when calling a trusted professional is the safer and smarter choice.
You're locked out of your home. Don't be tempted to force entry or break a window as a locksmith can gain access without causing damage to your door or lock. Read our guide on what to do if you're locked out for step-by-step advice.
You have a non-standard or high-security lock. Smart locks, multipoint locking systems (common on uPVC doors), and high-security mortice locks often require specialist tools and knowledge to replace correctly, it would be better to contact a local locksmith.
Your door has suffered damage. If a break-in has damaged the door frame, the lock mechanism, or the surrounding structure, a locksmith can assess the full extent of the damage and ensure everything is properly secured.
You want to upgrade your security. A qualified locksmith can advise on the best locks for your specific door type, your insurer's requirements, and the latest recommendations from the police.
You're simply not confident doing it yourself. There's no shame in that, many homeowners wouldn’t feel comfortable changing their own lock. An incorrectly fitted lock can leave your home vulnerable and may even invalidate your home insurance.
Whatever the situation, TrustATrader makes it easy to find a vetted local professional near you. Whether you need a locksmith in Birmingham or anywhere else across the UK, every trader in our directory is checked, insured, and backed by genuine customer reviews.
Final Tips for Keeping Your Home Safe
- Always keep at least one spare key with a trusted person rather than hiding it near your front door.
- Check that your locks meet your home insurer's minimum requirements, many policies specify British Standard or Sold Secure-rated locks.
- Consider fitting anti-snap cylinders if you have a uPVC door, these are widely recommended by police and insurers.
- If you're moving into a new property, changing the locks should be one of your very first actions. It's a small job to give you that peace of mind.
Looking for more home security advice? Explore related articles below or find a vetted locksmith near you on TrustATrader today.