How Can I Tell If My Double-Glazed Unit Has Failed?
Double glazing is a great way to keep your home warm and energy-efficient. But like anything else, it doesn’t last forever. One of the most common problems is a failed sealed unit—sometimes called a “blown window.” The good news? You don’t always need to replace the whole window—often, replacing just the glass unit will solve the issue.
What Are the Signs of a Failed Double-Glazed Unit?
Here are some clear signs your double glazing might have failed:
- Condensation between the panes: If you see fog or moisture trapped inside the window, the seal has likely broken.
- Misting or fogging that doesn’t wipe off: This often looks like a permanent cloudiness.
- Cold patches near the window: You may notice the area around the window feels cooler than the rest of the room.
- Visible seal damage: Look for cracked or shrunk seals around the edge of the glass.
- Distorted view: The glass might appear slightly warped or hazy in places.
Any one of these signs could mean the insulating gas between the panes has escaped, reducing both thermal efficiency and visibility.
What Causes a Sealed Unit to Fail?
Several common factors can lead to window seal failure:
- Age: Most sealed units last around 10–20 years, depending on quality and installation.
- Poor installation: If the unit wasn’t properly fitted, it’s more prone to early failure.
- Temperature changes: Expansion and contraction can weaken seals over time.
- Water ingress: Moisture getting into the frame can damage the seals.
Repair vs Replacement: Which Do I Need?
Once the seal has failed, unfortunately, it can’t be repaired. However, you don’t need to replace the entire window. In most cases, you can just replace the glass unit. This is called a sealed unit replacement, and it’s quicker, less disruptive, and significantly cheaper than replacing the full window frame.
There are exceptions. If the frames are also damaged, warped, or draughty, replacing the full window might be necessary.
Can I Do Anything Myself?
Yes, there are some simple checks you can do before calling in a professional:
- Wipe both sides of the glass to be sure condensation is between the panes (not just surface moisture).
- Check other windows—if only one or two are affected, it’s probably just those sealed units that need attention.
- Feel for draughts around the frame—this might indicate sealant or frame issues instead.
If you’re in doubt, it’s best to get a professional opinion. At Get My Windows Fixed, we offer free, no-obligation surveys to assess your double glazing and give honest advice.
How Much Does Replacing Just the Glass Cost?
Glass-only replacement is far more affordable than full window replacement. Costs vary depending on size, glazing type, and location, but most misted unit replacements fall between:
- £75 to £150 for a standard sealed unit
- £150+ for oversized, toughened, or shaped glass units
There’s no need to replace the frame if it’s in good condition—saving you money and hassle.
Need Help Diagnosing a Misty Window?
If your windows are misted, foggy, or showing signs of failure, we’re happy to help. At Get My Windows Fixed, we provide fast, friendly service across the UK, with expert guidance every step of the way. Our team can assess your glazing and let you know if a simple glass replacement is all that’s needed.