Common Signs Your Double Glazing Needs Repair

Why Double Glazing Fails in the First Place

Double glazing is built to last, but it does not last forever. A sealed unit is made up of two panes of glass held apart by a spacer bar, with the gap filled with air or argon and sealed around the edge with a specialist bond. That seal does the quiet, invisible work of keeping the cavity dry. Once it breaks down, moisture finds its way in and the unit can never really dry out again.

Frames have their own wear points. Hinges drop, handles work loose, gaskets harden and drainage channels block with grit and pollen. None of these things mean your windows were badly fitted — they simply mean they have been doing their job for a decade or two. The trick is catching the early warning signs before a small repair turns into a full window replacement.

Condensation Between the Panes

This is the clearest signal of all. Condensation on the inside of a room, or on the outside of the outer pane, is usually just a humidity issue and can be managed with better ventilation. Condensation between the panes, however, is a different matter entirely.

If you can see mist, droplets or a milky film trapped inside the sealed unit — and no amount of wiping or heating makes it go away — the seal has failed. It often shows up first as a small patch in one corner, then spreads across the glass as the seasons change. Left alone, the moisture can discolour the glass permanently and reduce the insulation value of the unit to roughly that of a single pane.

In most cases the frame itself is perfectly sound, and a qualified installer can simply swap the sealed glass unit while keeping the existing frame. That is a far cheaper job than replacing the whole window, and it can usually be done in under an hour per unit.

Draughts and Cold Spots Around the Frame

A gentle chill near a window is easy to dismiss, but it is worth investigating. Run the back of your hand slowly around the whole perimeter of the frame on a cold, windy day. Pay particular attention to the corners, the hinge side and the line where the frame meets the wall.

• Draughts through the opening edge usually point to worn or compressed gaskets, or a sash that no longer sits squarely in the frame.
• Draughts around the outer frame often mean the silicone or expanding foam behind the frame has perished, letting cold air in behind the plaster reveal.
• Cold patches on the glass itself with no visible draught may indicate the argon fill has escaped through a failed seal.

You may also notice higher heating bills, a room that never quite warms up, or curtains that move on a windy evening. These are all practical reasons to book an inspection rather than wait for winter to expose the problem further.

Stiff Handles, Dropped Hinges and Sticking Sashes

Handles should turn smoothly with light pressure. If yours needs two hands, a shove, or a particular knack, the locking mechanism is under strain. Common causes include a gearbox that has worn out, misaligned keeps, or a door or window that has dropped on its hinges over time.

Hinges are a frequent culprit on heavier doors and on wide windows. Look for visible wear on the hinge pins, a sash that catches on the sill, or a gap that is wider at the top than at the bottom. Friction stays and restricted opening mechanisms can also seize if they have never been lubricated.

These issues are rarely dangerous on their own, but they do matter. A window that cannot close properly is a security risk, and a door that will not lock is a problem you want sorted before the darker evenings. Most handle, hinge and alignment problems are quick, inexpensive fixes for an experienced fitter.

Cracked Seals, Perished Gaskets and Blocked Drainage

Take a close look at the black or grey rubber gaskets that run around the opening sash and the frame. Healthy gaskets are pliable and sit proud of their groove. Older ones go hard, shrink, split or pull away at the corners, and that is where draughts and water ingress begin.

Sealant around the external frame deserves the same attention. Cracks, gaps or a sealant line that has come away from the wall should be raked out and replaced before autumn rain finds it. While you are there, check the drainage slots at the bottom of the frame and the weep holes on doors. If water sits in the channel after rain, debris is blocking the path and it needs clearing.

Persistent damp around a frame can lead to mould on the internal reveal, stained plaster and, in the worst cases, rot in the timber behind. That is a far more expensive repair than a tube of sealant and a few new gaskets.

When to Call in a Qualified Installer

Some jobs are well within reach of a confident DIYer — a wipe-down, a drop of silicone spray on hinges, a clear-out of the drainage channels. But if you are seeing misted glass, a door that no longer locks, or water appearing where it should not, it is time for a proper inspection.

Look for a fitter who is happy to diagnose before they quote, who can tell you honestly whether you need a new sealed unit or a whole new frame, and who will put their findings in writing. Ask about guarantees on both parts and labour, and check that any replacement glass meets current energy efficiency standards.

Catching these signs early is almost always the cheaper route. A failed seal caught in its first winter is a straightforward glass swap; left for three or four years, it is often a new window. A quick check around your home each spring will tell you plenty — and if something looks amiss, a short conversation with a qualified installer will put your mind at rest.