Repair or Replace? A Homeowner’s Guide to Double Glazing Problems

*This is a collaborative post on double glazing problems

Your windows have started misting up. Or the handle sticks. Or there’s a draught creeping through the frame that you can feel from the sofa. The question every homeowner asks next is the same one: do I fix this, or do I need a whole new window?

The honest answer is that it depends on far less than most salespeople would have you believe. Plenty of problems that look terminal are actually cheap, quick fixes. Others genuinely do signal the end of a window’s working life. Knowing the difference can save you thousands.

What’s actually gone wrong?

Double glazing has three main components that can fail independently: the sealed glass unit, the frame, and the hardware. Most people lump them together and assume one failure means replacing the lot. It rarely does.

Misted or foggy glass

This is the classic complaint. Condensation appears between the two panes, where you can’t wipe it away. It means the perimeter seal has failed and moisture has found its way into the cavity, taking the argon gas with it.

Here’s the good news. The sealed unit can usually be swapped out on its own while the frame stays exactly where it is. A glazier measures the unit, orders a replacement, and pops it in. Typical cost sits somewhere between £70 and £180 per unit depending on size and glass spec, compared to £600 plus for a full window. If your frames are sound, replacing the glass alone is almost always the sensible call.

Draughts and water ingress

Draughts usually come down to perished gaskets or worn weather seals. These are rubber strips that harden over a decade or two and stop doing their job. Replacing them is a modest job and makes a noticeable difference to how warm a room feels.

Water getting inside is more serious. It might be a failed frame seal, a blocked drainage slot, or an issue with the surrounding brickwork rather than the window at all. Worth getting diagnosed properly before anyone quotes you for replacements.

Stiff handles, dropped sashes and dodgy locks

Mechanical faults are the most over-diagnosed problem in the industry. Hinges, handles, friction stays and multipoint locking mechanisms are all replaceable parts. A dropped or dragging sash is often just a hinge adjustment. If a company tells you a stiff handle means a new window, get a second opinion. A qualified double glazing repair specialist will normally sort hardware issues in a single visit.

When replacement genuinely makes sense

There are situations where throwing money at repairs is pouring it down the drain. Look for these signs:

Rotten timber frames. Once rot is structural rather than surface deep, filler is a delaying tactic, not a fix.

Warped or cracked uPVC. Older white uPVC from the eighties and nineties can go brittle and yellow. Cracks in the frame corners mean the unit has lost its structural integrity.

Multiple failures at once. If three of your four windows have blown units, the handles are all seizing and the seals are shot, you’re past the tipping point.

Single-glazed frames retrofitted badly. Some older conversions were bodged. They’ll never perform well.

You’re chasing energy savings. A 1990s double glazed unit might have a U-value around 3.0. Modern A-rated glazing sits nearer 1.2. That’s a genuine step change in heat loss.

The age test

As a rough rule, quality double glazing lasts 20 to 35 years. Below 15 years old, repair is usually the answer. Beyond 25, factor in that you’ll likely be spending again soon anyway.

Running the numbers

Average window replacement across a three-bedroom semi in the UK runs to somewhere between £4,000 and £8,000 depending on frame material, size and how many windows you’re doing. Repairs by contrast rarely top a few hundred pounds per window.

The calculation isn’t complicated. If repair costs come to more than roughly half the price of replacement, and the window is over twenty years old, replacing starts to look reasonable. If it’s a single blown unit in a ten-year-old frame, repairing is a no-brainer.

Don’t forget resale considerations either. Estate agents consistently report that visibly failed windows knock buyer confidence, but buyers don’t reward brand new glazing with a pound-for-pound uplift. Functional and tidy beats shiny and expensive.

Getting a straight answer

Always get at least three quotes, and be wary of anyone who inspects for ninety seconds and immediately recommends full replacement. Ask specifically whether the frame is sound and whether the problem can be addressed at component level. A reputable firm will tell you honestly, even when the smaller job is less profitable for them.

Check for FENSA or CERTASS registration for replacement work, since that covers your building regulations compliance. For repairs, look for a proper guarantee on parts and labour, ideally a minimum of twelve months.

Most window problems are fixable. Start there, and only reach for the chequebook when the evidence genuinely demands it.