Door lock

Just renewing house insurance and been asked the question as to whether entry doors have locks to BS3621. Front door has this marked, rear does not and key only has 3 "cut outs" if you see what I mean.

Got me to thinking I should replace this. It's a standard mortise lock (I think).

Are these standard sizes such that I remove the door furniture undo the screws from the lock, pull old one out and put new one in replacing door furniture?

...or is it more involved, this will answer whether I do it or get someone else!

Hi AJ
There's no reason why you couldn't do this yourself.

It sounds like you may have a three lever mortice lock. for insurance purposes you need a five (I believe.)

The case should be the same size as the existing (probably either a 2 1/2" or 3" case.

pull out the old one and see if the case is 65 or 67mm wide (it probably is and you can get new ones of the same size, also 75mm or 80mm which are less common). These are metric equivalents of 2 1/2" and 3" cases. Locks are made in very few standard sizes and a few odd ones.

If the old lock is a 3-lever one it will probably have a thinner case than the new one. You will need a sharp wide chisel to scrape out the mortice to fit, but don't start until you have bought your new lock.

It is usual for backdoor locks to be sashlocks, i.e. they also have a latch operated by a knob or handle as well as the key-operated deadbolt. It is usual for front door locks to be deadlocks (no knob, so when they are shut, they are locked) but you have not got to do it this way if you don't want to.

If you are willing to pay extra, you might consider buying a new front and back door lock, suited to the same key. This saves you having extra keys lying about the house or filling your pockets.

It is also a good idea for all doors except the final exit door to have rack bolts top and bottom to resist someone trying to break then in. These are much easier to fit than mortice locks as you only need a couple of drills (except for the small front plate which needs your small sharp chisel)

highly likely you'll need to widen the mortice to accommodate the wider BS rated lock - extra levers, and a layer of hardplate that prevents drilling. You'll also need to fit the keep that comes with the lock, so you'll also need to chisel out the frame to accommodate this. Not fitting the correct keep for the lock will invalidate its BS rating.

Thanks for all the advice. The new lock just slotted in. As suggested it was the hole for the striker plate in the frame that needed chiselling out but all now working fine. I'm glad I did it myself!