Window Lock Replacement and Mechanism Repairs in London

When a window won't lock, or won't open, the fault is usually hidden inside the frame. Most modern windows use a locking mechanism that runs along the opening edge of the sash, driven by the handle. When that mechanism wears or breaks, the handle may turn but the window stays loose, or the handle locks solid and the window won't open at all. Mark repairs and replaces window locking mechanisms on uPVC, aluminium and timber windows without replacing the window.

Espagnolette and shoot-bolt mechanisms replaced
Keeps realigned or replaced on the frame
Locking handles fitted
Fixed price confirmed before any work starts
Often same-day where the diary allows

The usual mechanism on uPVC casement windows is an espagnolette, often shortened to 'espag'. It is a metal strip with a gearbox in the middle where the handle's spindle fits, and locking points along its length. Turning the handle slides the strip, and the locking points engage with keeps fixed to the frame. Some windows use shoot bolts instead, which push rods up and down into the top and bottom of the frame. Either way, the window is only secure when every locking point meets its keep.

Telling the handle from the mechanism is the key question. If the handle turns loosely with no resistance and nothing moves, the gearbox inside the mechanism has usually broken. If the handle is stiff and the window feels tight to lock, the sash may have dropped so the locking points drag on the keeps, which a hinge or keep adjustment can fix. If the handle itself is snapped or cracked, a new handle is enough. Our guide to a window lock not working walks through these checks in more detail.

A window that is locked and won't open is the awkward case, because the mechanism has failed in the closed position. This needs care to release without damaging the frame or the glass, and is one of the jobs best left to a glazier. Once it is open, the old mechanism is removed and a matching one fitted to the same position, so the existing handle holes and keeps can usually be reused.

Mechanisms come in many backsets and lengths, and older windows sometimes use discontinued patterns. Mark identifies the right replacement from the sash edge, and where an exact match has gone, a modern equivalent can usually be fitted. For other uPVC window faults such as hinges, see our uPVC window repairs page.

Security is the other reason to act quickly. A window that closes but doesn't lock looks secure from the street but can be eased open, and an upstairs window that won't open can matter in an emergency. If several windows in the house were fitted at the same time, their mechanisms have usually done the same amount of work, so it is worth trying each handle while Mark is there.

How the repair works

1. Tell us what it does Does the handle spin, stick, or turn without locking? That points to the failed part.
2. Identify and price Mark identifies the mechanism and confirms a fixed price before work starts.
3. Replace and test Mechanism or keeps replaced, then every locking point checked to engage cleanly.

Frequently asked questions

Why won't my window lock?

Either the mechanism inside the frame has broken, the window has dropped so the locking points miss the keeps, or the handle has failed. Each has a different fix, which is why it helps to describe how the handle feels.

Can a window locking mechanism be replaced on its own?

Yes. The mechanism is a separate part fixed into the edge of the opening sash. It can be removed and replaced without changing the glass, the frame or usually the handle.

How do I know if it's the handle or the mechanism?

If the handle turns loosely and nothing moves, it's normally the mechanism. If the handle itself is cracked, snapped or wobbles on its fixings, it's the handle. A stiff handle often means the window is out of line.