Yes, you can repair double glazed windows, but only if the issue is limited to the frame, seals, or hardware, not the sealed glass unit itself. A failed seal that causes misting between panes typically requires replacing the sealed unit, not the whole window, according to the Energy Saving Trust (Energy Saving Trust, 2026).
The deciding factor is whether the double glazing has blown, meaning the airtight seal between the two glass panes has failed. This allows condensation, dirt, or argon gas to escape. If you see mist, fog, or water between the panes, the sealed unit is compromised and cannot be repaired. However, issues like broken hinges, faulty handles, draughty frames, or cracked putty can often be fixed without replacing the entire window. This applies to most uPVC, timber, and aluminium frames, but not to very old or non-standard units where replacement parts are unavailable.
Repairing a failed seal is not possible
Once the seal breaks and moisture enters the cavity, you cannot simply reseal it. The sealed unit must be removed and replaced with a new one. A typical replacement for a standard-sized double-glazed unit costs between £100 and £200, including labour, according to the Glass and Glazing Federation (Glass and Glazing Federation, 2026). This is far cheaper than replacing the entire window frame, which can cost £400–£800 per window. You should only consider the full replacement if the frame is also damaged or rotting.
Frames and hardware are often repairable
Draughty windows, sticky hinges, or broken handles are common and can be repaired by a competent DIYer or a window specialist. Replacing a hinge costs around £20–£50 for parts, while a new handle is typically £10–£30. The Fenestration Self-Assessment Scheme (FENSA) advises that repairs to frames and hardware do not usually require building regulations approval, provided the glazing itself remains intact (FENSA, 2026). However, if you replace the sealed unit, the work must comply with Part L of the Building Regulations for thermal performance.
When replacement is the only option
If the glass is cracked, the frame is warped, or the window is more than 20 years old, replacement is usually more cost-effective than repair. A new double-glazed window with an A-rated energy efficiency can save around £110–£145 per year on heating bills, based on Energy Saving Trust estimates for a typical semi-detached home (Energy Saving Trust, 2026). Also, if the window fails to meet current Building Regulations (minimum U-value of 1.6 W/m²K for replacement windows), you may need to upgrade rather than repair to stay compliant.
A worked example
A 1930s semi-detached house in Manchester with misted double glazing in the living room bay window would cost £180 to replace the sealed unit rather than £1,200 for a full window replacement. The homeowner noticed condensation between the panes last winter and called a local FENSA-registered installer. The installer removed the old unit and fitted a new A-rated double glazed unit with a warm-edge spacer bar. The job took 90 minutes and came with a 10-year guarantee. According to the Energy Saving Trust (Energy Saving Trust), replacing a blown sealed unit restores the window’s thermal performance to its original U-value of around 1.2 W/m²K. The household saves roughly £65 per year on heating bills compared to leaving the failed unit in place.Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6).
| Item | Figure |
|---|---|
| Upfront cost after grants | £180 |
| Yearly savings | £65 |
| Payback period | 2.8 years |
| 25-year lifetime savings | £1,625 |
What homeowners often get wrong
The most common mistake is assuming that misting between panes means the whole window needs replacing. Homeowners throw away perfectly good frames and spend thousands unnecessarily. Here are three pitfalls to avoid
- Believing you can reseal a blown unit Some companies claim to inject a drying agent or vacuum the cavity, but the Glass and Glazing Federation warns this never works long-term. The only proper fix is replacing the sealed unit, or you waste £150 on a temporary solution that fails within months.
- Ignoring a failed seal to save money A misted window loses up to 40% of its insulating value, according to Ofgem. Leaving it damaged costs you roughly £65 per year in extra heating bills and can lead to mould on the frame, which voids the manufacturer’s warranty.
- Assuming all frames need replacing too Even if the sealed unit has blown, the uPVC or timber frame is often fine. Replacing just the glass unit costs £100–£200, whereas a full replacement window costs £400–£800. You miss out on huge savings by not checking with a FENSA-registered installer first.
Quick reference
- Replacing a blown sealed unit costs £100–£200, far less than the £400–£800 for a full window replacement.
- A misted double glazed window loses roughly 40% of its thermal efficiency, adding about £65 to annual heating bills.
- Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6).
- Repairing a failed seal with a DIY kit or injection method is not recommended by the Glass and Glazing Federation and typically fails within six months.
- Frames, hinges, handles, and putty can usually be repaired for £30–£80 without touching the glass unit at all.
Frequently Asked Questions
Yes, but only for minor issues like lubricating hinges or tightening handles. For failed seals or broken glass, hire a professional, advises the Glass and Glazing Federation.
Repairing a sealed unit costs between £100 and £200, according to the Glass and Glazing Federation. Full window replacement can cost £400–£800.
A blown double glazed window shows mist, fog, or water between the glass panes. This indicates the airtight seal has failed and the sealed unit needs replacing.
