Signs Your uPVC Door Gearbox Is Failing (and the 30-Second Test)

The gearbox (or centre case) is the box in the middle of a multipoint lock, where the handle and key go. When you lift the handle or turn the key, it drives all the hooks, rollers and bolts along the edge of the door at once. It usually fails slowly, with small warning signs first, which is why it's worth catching early.

Warning signs your gearbox is wearing out

• The handle droops or feels floppy. The spring inside the gearbox (or the handle) has weakened.
• Lifting the handle takes more force than it used to. Something is dragging, either inside the gearbox or because the door is out of line.
• You have to push or pull the door to get it to lock. A classic alignment problem, and the main cause of gearbox wear.
• The key turns but nothing happens, or turns further than it should.
• Clicking, grinding or crunching from inside the door when you use the handle.
• The handle lifts but some locking points don't come out fully.

If the handle now spins freely or does nothing at all, the gearbox has usually already failed.

The 30-second test: gearbox or door alignment?

Open the door, then lift the handle and turn the key, and watch the edge of the door:

Why gearboxes wear out

• Forcing the handle on a misaligned door. This is the big one. When a door drops, even by a few millimetres, the hooks and rollers no longer line up with the keeps on the frame. You end up leaning on the handle to make it lock, and all that force goes through the gearbox. Do that twice a day for a year or two and something gives.
• Everyday wear. Every lift of the handle moves the parts inside. Eventually the spring weakens and the parts wear.
• A dry mechanism. With no lubrication, everything works harder.
• Temperature changes. uPVC expands and contracts with the seasons, so a door that's slightly out of line can catch in hot or cold weather and be fine the rest of the year.

What to do about it

If it's alignment

Get the door lined up so the locking points slide into the keeps without forcing. Usually that means adjusting the keeps on the frame, or adjusting the hinges to lift a door that's dropped. It's a much smaller job than a new gearbox, and it protects the one you've got. A spray of light lubricant on the locking points and keeps helps too.

If it's the gearbox

Replace just the gearbox. It's far cheaper than a full lock, and most fit your existing strip. You'll need the brand, the PZ (usually 92mm), the backset (usually 35mm) and whether it's single or split spindle. Our guide to identifying your multipoint lock shows you how to measure, and our guide to replacing a uPVC door gearbox takes you through the swap.

About 4 in 5 of the 400+ gearboxes we sold online last year were GU or ERA.

If a locking point has broken

You'll need a full multipoint lock. They're too long to post, so we supply them from our trade counter in Aintree. Email us a photo of the full length of the lock and we'll match it.

Our best-selling gearbox

GU Old Type, 35mm backset, 92mm PZ, single spindle. £14.99.

View the gearbox →

Door stuck locked?

If the gearbox fails with the door locked shut, don't force it. Leaning on the handle or kicking the door can damage the frame and turn a gearbox job into a new door. A locksmith can open it from outside, usually without damage, and you can then fit a new gearbox yourself.

That's the best reason to act on the early signs: a gearbox is a quick swap while the door still opens.

Landlords: check the gearbox at every change of tenant

A gearbox that fails between tenancies can mean an emergency call-out or a delayed move-in. Before each let, take a minute to:

• lift the handle and turn the key with the door open, then shut. Both should feel smooth, with no difference between the two
• listen for clicking or grinding inside the door
• check the handle springs back to level and doesn't droop
• ask the outgoing tenant whether the door has been stiff to lock

If anything feels off, swap the gearbox now, while the door still opens.

Need help?

Send a photo of your gearbox and faceplate (the metal strip on the edge of the door) to info@homesecureshop.co.uk, or call us on 0151 521 8089. We'll tell you which gearbox you need.