Posted on January 18, 2021 13:55 by matan

How To Change A Lock

Why it is risky to change your own lock

There are several reasons why it is risky to change a door lock yourself. Perhaps the first and most important is that you may invalidate your insurance if you fit the wrong lock if you are subsequently burgled. Also, by having your lock replaced professionally, you will have a guarantee and after-sales service that you won’t have if you fit it yourself. Besides, you need to understand the different lock standards, and you have to choose a replacement lock that is compatible with the handle you are using. 


We do not advise replacing a lock yourself, but to give an idea of the processes involved we have put together a ‘how to do it’ guide. 


Different types of lock

How you change a lock depends on the type of lock you are trying to change.


Mortice locks

There are two types of mortice locks; a mortice sash lock, which has a latch and bolt, and a mortice deadlock which only has a bolt.


If you want to change this type of lock yourself, there are some measurements you need to do so that you buy the correct replacement lock. 

  • On the door’s outer face, measure the distance between the edge of the door and the centre of the keyhole. If it measures 45mm, you will need to buy a 65mm mortice lock. If the distance is 57mm you will need a 75mm lock. 

  • When replacing a sash lock, the next measurement is from the keyhole’s centre to the door handle spindle hole. 

  • Third, measure the height of the faceplate on the edge of the door. You now have the measurements you need to buy a replacement lock.

  • Remove the faceplate by undoing the screws. 

  • If you are replacing a sash lock, you will have to remove the handles and their connecting spindle. If you shoot the bolt out, you can remove the lock mechanism by gripping the bolt. 

  • Ensure the new lock matches the old one, then slide the new lock into position and screw in the new faceplate. Make sure the new faceplate is flush with the edge of the door. 

  • If you are working on a sash lock, you can now replace the handles. 

  • Now turn to the door frame, and remove the strike plate. 

  • Close the door gently against the frame with the lock bolt out, and mark on the frame where the bolt meets it. 

  • See if the position of the box which holds the bolt is correct. If not re-cut the box to the right position and depth. 

  • Fit the new strike plate and screw it into position. 

  • Check the lock operates correctly with the door open, then close the door and test it again.


Euro cylinder locks

There are different types of the euro cylinder lock. Some have a key slot on each side, and others have a key slot on the outside, and a thumb turn on the inside. 


Now you have to do some measurements. You need to know the length of your old lock so that you know what size to buy. 

  • You have to measure the distance from one of the centre screws, which you will find above and below the bolt, to the lock’s outer end on each side. You can now buy a replacement euro cylinder with the right measurements.

  • Now open the door and remove the cylinder retaining screw, which you will find below the bottom centre screw. 

  • Loosen the screws on the handle backplate to reduce the pressure on the lock. 

  • Insert the key in the old lock and slightly turn it to left and right to align the cam tongue with the barrel of the lock. If you gently pull the key back towards you while turning, you should be able to feel when the tongue is aligned because the lock will start to come out. 

  • With the old lock removed, you can insert the new lock and do up all the screws.


Rim cylinder locks

You can identify a rim cylinder lock quite easily. It sits on the inner face of the door with its thumb turn nightlatch. The keyhole, on the outer door face, is part of the cylinder of the lock. 


  • To replace the lock first remove the screws which fix the nightlatch to the inside of the door. You can then slide the nightlatch off the cylinder bar. 

  • With the nightlatch removed you can see the screws of the cylinder fixing plate. Remove these screws, then pull the cylinder out from the front of the door.

  • Make sure that the new cylinder you buy looks the same as the cylinder you have removed. Also ensure that the new cylinder bar that connects the cylinder to the night latch is the same length as the old one. If not, you have to cut it to the right size.

  • Push the new cylinder through the hole in the front of the door. Secure it with the screws through the cylinder fixing plate, which you removed earlier. 

  • You can now replace the nightlatch using its fixing screws. 

  • With the door still open, insert the key and test the lock to ensure it works properly. 


Keys4u are always available via the phone or email to help you with any security issues you may have. 


Tel 033 330 52993

Email[email protected]


Related services

Door Lock Installation 

Door Lock Upgrade 

Security Upgrades

Window Lock Replacement And Repairs

Door Lock Replacement