Can You Repair Blown Double Glazing

Yes, in almost every case.

A blown double glazed window needs a new sealed unit, not a new window, and the fix costs a fraction of a full replacement. You won’t need to replace the entire window frame, just the failed glass unit inside it.

The word “blown” sounds serious, like something has failed structurally.

In reality it just means the seal around the glass has given way.

What blown double glazing means – By Edinburgh double glazing experts

A double-glazed window has two panes of glass with a gap between them, usually filled with argon gas to improve insulation.

That gap is sealed shut at the edges.

When the seal breaks down, moisture gets into the gap. You’ll see mist, fogging, or a milky haze between the panes that won’t wipe away from either side of the glass.

That’s different from ordinary condensation on the room-side of the glass, which comes from cooking or drying washing indoors and wipes off easily.

Condensation inside double glazing, trapped between the panes, is the real sign the unit has blown.

Failed double glazing and condensation inside the unit almost always go together, since the broken seal is what lets the moisture in.

Why double glazing blows

Every sealed unit contains a strip called a spacer bar, packed with a moisture-absorbing material called desiccant.

It’s designed to soak up any trace moisture left in the unit during manufacture.

Over time, particularly in older windows, the edge seal degrades from repeated expansion and contraction as temperatures swing between summer and winter.

Once the seal lets moisture in, the desiccant inside the unit eventually saturates and stops working.

That’s what causes double glazing to fail in almost every job we handle.

A 15 to 20 year old double glazing unit is the most common candidate.

Poor installation or a manufacturing fault can cause it much sooner, but wear and tear on the seal is the root cause almost every time.

Installation quality makes a difference

Poorly fitted or lower-grade units are especially prone to early failure. The sealant used at the edge doesn’t always hold up as well as it should.

Weak window seals are the single biggest reason units fail early, more than any other factor.

A well-installed unit from a reputable installer tends to last much longer before the seal starts to go.

Across the units we replace, age and weather exposure wear the seal down long before anything else in the window fails.

Signs your glazing has blown

The clearest sign, and the first thing we check for on a call-out, is condensation between the panes that’s always there, whatever the weather.

It often looks worse first thing in the morning or after a cold night.

You might also notice a faint white or grey staining creeping in from the edges of the glass. That’s the desiccant residue baking onto the inner surfaces over time.

Some windows show reduced clarity or a slight distortion when you look through them at an angle. That’s usually a sign the argon gas fill has escaped through the failed seal.

None of these signs mean the window itself is unsafe. They just tell you the sealed unit has reached the end of its working life.

It’s not only windows that blow

Conservatory roof panes and patio doors use the same sealed-unit construction, so their glass units can also become misty and foggy.

Misted double glazing and glass panes with visible staining are usually easy to spot once you know what you’re looking for.

Can blown double glazing be repaired?

Almost always, yes.

A blown unit gets replaced with a new, factory-sealed glass unit that fits straight into your existing frame. The frame, hinges, and handles stay exactly where they are.

This is a glass unit replacement, not a full window replacement. Nobody needs to touch your brickwork, plaster, or décor.

We cover exactly how that double glazing repair process works on our guide to replace a double glazed window.

The repair or replacement decision almost always comes down to the frame, not the glass. If the frame is sound, repair is the answer.

When it isn’t a straightforward repair

The rare case where we don’t recommend repair is when the window frame itself has failed.

A cracked, warped, or rotten frame needs replacing regardless of what’s happening with the glass, but that’s a frame problem, not a blown-unit problem.

Replacing the entire window unit, frame and all, is a much bigger job than swapping the glass.

A complete replacement of the windowpanes and frame together is the exception here, not the rule.

Sealed units are made to measure, so the size of the window or an older frame doesn’t rule out a straightforward glass unit replacement.

A single blown unit can usually be swapped out in under an hour.

That’s a far smaller job than the phrase “window replacement” suggests.

What happens if you leave a blown unit unrepaired

A blown unit on its own won’t fall out or become unsafe. But it keeps losing heat and pushing your bills up even though nothing looks obviously wrong.

The insulating gas that made your double glazing energy-efficient has usually escaped, so the window’s insulation performance drops close to that of a single pane.

That shows up as higher heating bills and a colder room near the window.

Persistent condensation between the panes can also encourage mould on the surrounding frame and sill if it’s left for long enough.

The higher bills and the mould risk both continue until the unit is replaced.

Draughts around the window panes often get worse too, on top of higher energy bills.

Whether it gets repaired or replaced, the window needs to insulate the room properly again.

Warranty, guarantee and insurance

Some double glazing installers offer a guarantee that covers sealed unit failure for a set number of years.

Check any paperwork from when the windows were originally fitted to see if yours are still covered.

Home insurance rarely covers blown double glazing, since it’s treated as wear and tear rather than accidental damage. That means the repair usually gets paid for directly, without a claim.

If your windows came from a national installer that’s since gone out of business, any guarantee they offered is worth little in practice.

An independent double glazing expert can still repair the unit regardless of who originally fitted it.

Every repair we carry out comes with our own 5-year guarantee, helping you feel secure on our experienced handy work.

Preventing it happening again

You can’t stop a sealed unit ageing forever, but a few habits reduce the risk of blown units elsewhere in the house.

Keep drainage channels at the base of the frame clear so water doesn’t sit against the seal.

Avoid pressure-washing windows directly, since forcing water at the glazing bead can push moisture towards the seal over time.

And if one unit in a window has blown, keep an eye on its neighbours, since they’re usually the same age.

Cold air finding its way in around a frame is often the first clue that a neighbouring unit is starting to go too.

Catching it early is usually the best way to fix it before the whole window needs replacing.

Common questions about blown double glazing

Can blown double glazing be repaired, or does it need to be replaced?

It can be repaired in the vast majority of cases, by fitting a new sealed unit into the existing frame. Full window replacement is only necessary if the frame itself has failed.

How can I tell if my double glazing has blown?

Look for double glazing condensation between the two panes that never clears, even on dry days. If it wipes away from the inside or outside surface, that’s ordinary room condensation, not a blown unit.

Are DIY repair kits effective for blown double glazing?

Not really. DIY misted double glazing kits work by drilling a small hole and injecting a drying agent, which might clear the fog temporarily. But it doesn’t restore the seal or replace the lost argon gas. The misting typically returns quickly once the drying agent is exhausted.

Does repairing blown double glazing improve energy efficiency?

Yes. A new sealed unit restores the insulating gas fill and the airtight seal. That brings the energy efficiency of your windows back close to their original specification.

Get your windows checked properly with Totalseal Repairs

A foggy window is almost always worth fixing rather than replacing, it is far cheaper and means you get to keep your original window frame.

If you’re not sure whether it needs replacing or just a straightforward repair, we can take a look and tell you honestly.

We’re owner-operated, not a call centre, and we don’t sell replacement windows. There’s no incentive to recommend one when we can repair double glazing instead.

We restore your windows to full working order, and we’re upfront about repair or replacement costs from the first visit, with no hidden extras.

We repair blown, misted, and cracked double glazed windows and doors across Central Scotland.

Every job comes with over 30 years of experience behind it and a 5-year guarantee.

Call us on 07977 463 139 for honest advice. You can also reach us through our contact page for a free, no-obligation quote.