Guide
Runcorn Door Lock Types Explained: What Each UK Lock Is and Where It Fits
One question comes before everything else on this page: is the lock stopping you getting in or out, or securing the door, right now? If so, skip the reading and call 01928 611001, because emergency calls are taken 24 hours a day, every day of the year. If you simply want to put a name to the lock in front of you before buying a part or booking a job, read on.
The doors of UK homes generally carry one of four lock families, and which one you have was settled by the door rather than by anyone's preference: the mortice lock, the nightlatch worked by a rim cylinder, the euro cylinder driving a multipoint mechanism, and the humble surface bolt. This guide explains each one, shows you how to recognise it, and decodes the jargon on a product listing. From Runcorn Locksmith, it names types rather than recommending products, quoting prices or telling you which lock to buy.
Call with your postcode for a current arrival estimate.
- 24-hour emergency cover
- No call-out charge
- Price agreed before work starts
Every UK Door Lock Type at a Glance
When a lock needs repairing or replacing, one of the first things you are likely to be asked is what type it is, and the keyhole on its own rarely settles that. The door is the better starting point: what it is made of, where the mechanism sits, and what shows on the inside face and along the edge. The table below covers the lock types found on UK domestic doors, and the quickest way in is the middle column.
| Lock type | Door it is normally found on | How to recognise it | Usual name on a listing | Does a British Standard commonly apply? |
|---|---|---|---|---|
| Mortice deadlock | Timber, usually external | One keyhole on each face, case hidden in the door edge, no handle | Mortice deadlock, often with a lever count | BS 3621 can apply to the lock; check the faceplate |
| Mortice sashlock | Timber, external or internal | Keyhole plus a square hole for the handle spindle, case in the edge | Mortice sashlock | BS 3621 can apply to some versions; check the faceplate |
| Nightlatch with rim cylinder | Timber, usually the front door | Round keyway outside, box-shaped case on the inside face | Nightlatch, rim lock or deadlocking nightlatch | Some versions are made to a British Standard; check the case |
| Euro cylinder in a multipoint | uPVC, composite, aluminium, and now some timber | Narrow keyway with a rounded top, long metal strip down the door edge | Multipoint lock, uPVC door lock, euro cylinder | BS 3621 does not usually apply; TS 007 may be relevant to the cylinder |
| Euro cylinder in a standalone case | Timber, aluminium and some commercial doors | Euro keyway feeding a single lock case rather than a strip | Euro profile sashlock or deadlock | Depends on the case; check the product |
| Surface-mounted door bolt | Any, usually on the inside | Manual slide bolt screwed to the face, no key | Door bolt, tower bolt or barrel bolt | Not usually sold against a lock standard |
| Mechanical push-button lock | Communal and office doors | Keypad of buttons, no keyway | Push-button or digital mechanical lock | Check the product |
The middle two columns are the ones people most often get wrong, so each has a section of its own below. For what the British Standard on door locks covers, see the standards guide, and if you already know what you want fitted, see having a lock fitted.
Locks Fitted Into a Timber Door
A timber door usually carries one of two things, a lock set inside its edge or a latch mounted on its inside face, and quite often both on the same door. A traditional rim lock can also sit on that inside face. Orientation is the quickest test: if the keyhole goes into the edge of the door, you are looking at a mortice lock, and if the key passes through the face into a box on the inside, it is a nightlatch. Neither is better; they do different jobs, which is why older front doors often have one of each.
Mortice Deadlocks and Mortice Sashlocks
The difference fits in one line: a deadlock has a bolt and nothing else, while a sashlock has a bolt and a latch, so a sashlock also takes a handle. Both sit in a recess cut into the door edge, and with the door open you will normally see a metal faceplate with a bolt, a latch or both showing through it.
A deadlock is worked by key from either side and only holds the door shut when it is locked, so it is usually paired with a separate latch or nightlatch that keeps the door closed the rest of the time. A sashlock does both jobs in one case: the handles work the spring latch and the key works the bolt, which is why it is the usual fitting on a door that needs a handle and a lock together.
| Deadlock | Sashlock | |
|---|---|---|
| Keyhole | One | One |
| Square spindle hole | None | Yes, above or below the keyhole |
| Handles | No | Yes |
One naming point carries into the next part of the guide: the lever count in the product name is the number of levers inside the case. Sizing one up to buy a replacement is covered under measuring a mortice lock before you buy one.
Nightlatches and Rim Cylinders
A nightlatch is the box on the inside of the door that latches by itself as the door closes, operated from outside by a rim cylinder. Because the case is fixed to the inside face, its spring latch can meet a keep on the frame without anything being cut into the door edge. It has a few parts worth naming:
- Rim cylinder: the round keyway on the outside face, linked through the door by a flat tailpiece.
- Case and spring latch: the box on the inside, and the tongue that drops into the keep on the frame.
- Inside control: a knob or handle that releases the latch from indoors.
Cylinder and case are often sold separately, so a worn cylinder can be changed alone. A deadlocking nightlatch goes a step further: it can be locked so the latch cannot be slipped, and some versions add a key-locking handle on the inside. If yours has stopped behaving properly, see a latch or lock that has stopped working properly. A rim lock is not always the same thing as a nightlatch: it may hold a latch, a bolt or both, may not latch on its own when the door shuts, and may be worked by key, handle or knob. A plain nightlatch on its own is not usually what is specified for a final exit door, which is one reason so many timber front doors carry a mortice deadlock as well; what policies actually ask for is covered in the standards guide.
Multipoint Locks Are Not One Type
On a uPVC or composite door the lock is a metal strip running much of the height of the door edge, and makes are not interchangeable. The governing point is simple: the euro cylinder is the part the key turns, the multipoint is the strip the handle drives, and anyone asking about uPVC door lock types is nearly always asking about the strip. Identifying it is one thing; ordering a replacement needs a full set of measurements, which the uPVC cylinder guide covers.
What the Strip Itself Tells You
The answer is usually stamped on the metal strip in the door edge, which you can see with the door open. Four things are worth looking for:
- The maker's name. Common UK names on these strips include GU Ferco, Avocet, Mila, ERA and Fullex, listed here purely as identification marks and not as a ranking.
- The PZ. The distance from the centre of the spindle to the centre of the keyhole.
- The backset. The distance from the centre of the keyhole to the edge of the strip.
- The spindle. A split spindle behaves differently from a single one, because it restricts what the outside handle can do.
Home Secure's uPVC multipoint identification guide sets out these markers. They identify the pattern; ordering a replacement needs the full set, which is covered under changing the cylinder on a uPVC or composite door.
The Locking Points, and Why They Differ
The lumps spaced along the strip are its locking points, and their shape is part of what identifies the lock. The common styles are:
- Rollers, which draw the door in against its seal.
- Mushroom rollers, which do the same job and also resist the door being levered.
- Deadbolts, which throw straight into the frame.
- Hooks, in small and full sizes, which bite into the keep so the door cannot be pushed sideways.
A strip with hooks and mushroom rollers is doing more work than one with plain rollers, which can be the real difference between two doors that look identical outside. When the handle lifts and nothing engages, the fault usually lies in the gearbox driving these points rather than the points themselves; uPVC door lock repair and replacement deals with that.
A cylinder is the key-operated part, not the whole lock: it reads the key and passes the movement to a gearbox, a mortice case or a nightlatch behind it. The euro profile is narrow with a rounded top and turns up on uPVC, composite and aluminium doors, and on some timber ones too. Changing a cylinder can alter which keys work the door and may strengthen it against certain attacks, but it will not fix a worn gearbox, a damaged strip, a loose handle or a door that has dropped out of line.
Standards here are often misunderstood. BS 3621 is a performance standard for thief-resistant, mechanically operated single-point lock assemblies that need a key to lock and unlock from both sides, so it is not normally the standard for a multipoint strip. The current version is BS 3621:2017+A1:2024. Where a lock opens from the inside without a key, a different standard may apply, because BS 3621 specifically covers key-operated egress.
How to Read a Lock's Name
A lock's product name is four or five facts in a row, and they nearly always come in roughly the same order. Take a made-up listing such as "Maker 5 Lever Mortice Deadlock BS 3621". Read it left to right: the maker, then the lever count, then where it fits (mortice, inside the door edge), then what it does (deadlock, bolt only), then the standard it claims. Cylinder listings follow a similar pattern, which is explained in why anti-snap cylinders are named the way they are.
Lever Counts and What They Actually Mean
The number in front of the word lever is how many levers sit inside the case, and more levers allow more possible key combinations. Three lever locks are normally chosen for internal doors and lighter duty, five lever locks for external doors. Screwfix notes that three lever locks are not approved to BS 3621 because they are less secure, while five lever versions typically carry that designation.
| 3 lever | 5 lever | |
|---|---|---|
| Typical use | Internal doors, lighter duty | External doors |
| BS 3621 | Not approved | Often, but only if marked |
The caveat retailers skip: a five-lever lock does not automatically comply with BS 3621, because the standard tests far more than levers. Read the number and the standard as separate facts. If the lock you have is failing rather than just unidentified, see deciding whether a lock needs repairing or replacing.
The Marking on the Faceplate
The evidence lives on the faceplate, the metal strip you see in the door edge when the door is open. Screwfix states that locks compliant with BS 3621 carry a British Standard Kitemark and a number beginning BS 3621 engraved there, so a claim on a listing can be checked against the lock itself. You may find:
- The maker's name and sometimes the lever count.
- On a compliant lock, the Kitemark and the BS 3621 reference.
- On a uPVC strip, the maker and the pattern.
Look there before you trust a listing or a quote. A compliant lock will normally show BS 3621 on the product or its packaging, often next to a certification mark; if you cannot find the full standard reference and marking on the lock or its original paperwork, do not assume it is there. What the standard tests, and what it means for cover, is covered in the BS 3621 guide.
To match a name to your own lock, look at parts visible with the door open; nothing needs dismantling. Even with the brand identified, you may need measurements, a code and photographs showing the complete mechanism to establish the exact model.
- Door-edge faceplate: check this metal plate on mortice and multipoint locks for stamped markings, which may include a code, series name, logo or maker's name.
- Inside case: a nightlatch or surface rim lock may show its brand or model on the body.
- Cylinder face: look beside the keyway for a security marking or logo; either may appear on euro, oval and rim cylinders.
Which Type Belongs on Which Door
The rule behind everything on this page is that the door decides the lock, not the other way round.
Timber external door
normally a mortice lock, often with a nightlatch as well.
uPVC or composite door
normally a euro cylinder in a multipoint strip, operated with handles.
Aluminium door
normally a multipoint or a narrow-stile case.
Internal timber door
a lighter mortice latch or sashlock, or a bathroom lock with a thumbturn.
Communal or office door
sometimes a mechanical push-button lock.
Two exceptions are worth naming. Timber doors are now built with multipoints too, so the age of a door can tell you more than its material. And a flat entrance door onto a shared corridor is a case of its own, because it commonly needs to open from the inside without a key; why a flat entrance door takes a different lock is explained on our area pages.
Knowing the family still does not tell you which part has failed or what should replace it. Similar-looking locks can differ in size, operation, specification and compatibility, and a stiff key or loose handle could come from the cylinder, case, gearbox, spindle or door alignment. Replacing a single part with a compatible one, or adjusting the door, can often resolve the fault while leaving the rest of the system in place.
Types You Will Meet Less Often
A few more types turn up on UK doors, normally alongside a main lock rather than instead of one.
Surface-mounted door bolts
manual bolts on the inside face that add a second fixing point.
Hinge bolts
fixed studs on the hinge edge that resist that side being forced.
Mechanical push-button locks
common on communal and office doors.
Electronic and smart locks, access control and master key suites fall outside this guide and outside the work we do. Otherwise, the matrix above is the practical summary.
Not Sure What You Have? Ask Us
We will identify what is fitted, explain what repairing or changing it involves, and price it before anything starts. You do not need the model name; details about the door beat a guess. Have ready what the door is made of, whether it is open, shut or locked, where the keyhole sits, and a photograph of the faceplate with the door open.
- No call-out charge, at any hour
- Emergency calls taken 24 hours a day, every day of the year
- [PROVIDER PACK: DBS check evidence for technicians]
- [PROVIDER PACK: insurance held and evidence]
- A price on the call from what you describe
Ask What Lock You Have: call or message Runcorn Locksmith on 01928 611001.
Door Lock Type Questions
How can I tell what type of door lock I have?
Check three things: what the door is made of, where the mechanism sits, and what shows along the door edge. Timber doors commonly carry mortice locks, nightlatches or rim locks, while uPVC and composite doors often use a cylinder linked to a multipoint, though material alone does not prove it.
What is the difference between a mortice lock and a nightlatch?
The recess cut into the edge of the door houses the mortice lock. A nightlatch has a visible case fixed to the inside face. A timber entrance door can carry both, so finding one does not rule out the other.
Is a five lever lock the same as a BS 3621 lock?
No. Five lever describes the mechanism inside the case and does not prove compliance with BS 3621. Either the lock itself or its original paperwork should provide the evidence you need: the complete standard reference and the certification marking.
What lock does a uPVC door use?
A multipoint mechanism is the usual arrangement on modern uPVC entrance doors, with handles and a euro cylinder operating it. The cylinder is only one part of that system; the gearbox, the strip, the hooks and the keeps make up the rest.
My lock only works with the door open. What does that suggest?
It often points to the latch, bolt or locking points not meeting the keeps on the frame properly. Before deciding that a replacement lock is needed, investigate whether the door has moved, the hinges are worn or the alignment is poor.
Can a photograph identify my lock?
Often it can identify the general type, and it may narrow down the maker or model. A clear shot of the open door edge and the cylinder face gives the best chance.