Replace a euro cylinder lock

Swap a worn euro cylinder for a new one so your door locks smoothly and meets common insurance standards.

RL-01Prop the door open and gather your toolsOpen the door fully and prop it so it can't swing shut and lock while you work. You'll need a screwdriver (usually Pozidriv), a tape measure, and the new cylinder. Never remove a cylinder with the door shut, or you could lock yourself out.

RL-02Measure the old cylinder before buying a replacementFind the small screw on the edge of the door (the escutcheon plate on the door edge, not the handle). Undo it, then pull the cylinder out with the key still turned slightly. Measure both halves from the centre screw hole to each end in mm — cylinders come in matched pairs like 35/45, so getting this wrong means it won't fit.

1 each · Tape measure

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RL-03Buy a matching cylinder — check the BS kitemarkBuy a euro cylinder with the exact same measurements as the old one. If this door is a final exit door (front or back door), many home insurance policies require a cylinder rated BS3621 — check the box for the kitemark. If you're not sure whether your policy needs it, buy BS3621-rated anyway; it costs little extra.

RULES

1 each · Euro cylinder lock (matching size, BS3621 rated)

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KNOW THE RULES

This isn't a building regulation, but many UK home insurance policies require BS3621-rated locks on final exit doors. Check your policy or you may find a claim refused after a break-in.

RL-04Remove the old cylinderWith the door still propped open, undo the fixing screw on the door edge fully and set it aside. Turn the key about a quarter turn to release the cam, then pull the whole cylinder out from the outside face of the door. Keep the old cylinder to hand until the new one is fitted and tested, in case you need to swap back.

RL-05Fit the new cylinderSlide the new cylinder in from the outside, lining up the cam with the mechanism inside so it sits flush both sides. Insert the fixing screw and tighten it snugly — don't overtighten, as this can distort the cylinder and make the key stiff. Turn the key gently to check the cam moves freely before you fully tighten.

RL-06Test the lock from both sidesWith the door still open, test the key from both inside and outside, and check the handle and any thumbturn work smoothly. Then close the door and test locking and unlocking it properly before you rely on it. If the key sticks, back off the fixing screw slightly rather than forcing the key.

RL-07Tidy up and store spare keys safelyWipe down the door edge and handles where you've been working. Put the old cylinder somewhere safe until you're confident the new one is working well, then dispose of it. Keep spare keys somewhere sensible — not taped near the door.

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