If you have noticed mist or condensation trapped between the glass panes of your double glazing, the seal has failed. Here is the single most important fact: you almost certainly do not need to replace the whole window. Repair is usually possible at a fraction of the cost.
Repairing a failed double glazing seal costs £80-£120 per window in 2026, compared to £200-£500 for full replacement. The Glass and Glazing Federation confirms that replacing the sealed unit is usually possible without touching the frame.
- Repair costs £80-£120 per window, replacement costs £200-£500.
- Mist between panes that cannot be wiped means the seal has failed.
- The Glass and Glazing Federation says repair is usually possible without replacing frames.
- GOV.UK confirms repairing the sealed unit is more cost-effective than full window replacement.
- Check the frame condition first; damaged frames may need full replacement.
- The single most important fact about failed double glazing repair
- How to tell if your double glazing seal has failed
- Failed double glazing repair the two main options
- Quick numbers costs, savings, and energy impact
- Who pays for failed double glazing repair? Grants and eligibility
- How to verify your installer for failed double glazing repair
- Failed double glazing repair the direct answer for homeowners
- When replacement is the only option for failed double glazing
For a typical UK home, repairing a failed double glazing seal costs between £80 and £120 per window in 2026, compared to £200 to £500 for a full replacement. The repair method depends on whether the sealed unit can be fixed or must be replaced entirely, but repair is generally cheaper, faster, and does not require planning permission.
The single most important fact about failed double glazing repair
A failed seal, which shows up as condensation between the panes that cannot be wiped away, does not mean your windows are beyond saving. The Glass and Glazing Federation (GGF) states that in most cases the sealed unit can be replaced without touching the frame (GGF technical guidance, 2026). GOV.UK home energy efficiency advice confirms that repairing or replacing the glass unit is often more cost-effective than full window replacement (GOV.UK, 2026).
However, not all windows are suitable for repair. If the frame itself is damaged, or if the window is very old, replacement may be the only option. The key is to identify the cause of the failure first.
How to tell if your double glazing seal has failed
The clearest sign is visible condensation between the two glass panes that you cannot wipe off. This appears as mist, fog, or a cloudy layer that persists regardless of the room’s humidity level. The Energy Saving Trust explains that a failed seal allows moisture-laden air to enter the gap between panes, causing this condensation (Energy Saving Trust, 2026).
A second sign is reduced thermal performance. The window may feel noticeably cold to the touch in winter, because the insulating layer of argon gas or dry air has been lost. The GGF consumer leaflet advises that if you can see condensation between panes, the sealed unit has failed and should be repaired or replaced to restore energy efficiency (GGF consumer leaflet, 2026).
Failed double glazing repair the two main options
There are two main approaches to fixing a failed double glazing seal.
Option 1: Replace the sealed unit only. This is the most common repair. A glazier removes the glass panes, installs a new sealed unit with a fresh desiccant and gas fill, and reseals the frame. The GGF member pricing survey for 2026 puts the typical cost between £50 and £150 per window, with an average of £80 to £120 for a standard 600mm x 900mm unit, including labour (GGF member pricing survey, 2026). Checkatrade average cost data supports this range (Checkatrade, 2026).
Option 2: Full window replacement. This is necessary if the frame is rotten, damaged, or warped. It is also required for windows installed before 2002, which often have non-replaceable sealed units due to obsolete manufacturing standards. Full replacement costs £200 to £500 per window, depending on size and material.
Quick numbers costs, savings, and energy impact
| Measure | Typical value | Source |
|---|---|---|
| Repair cost per window (typical range) | £50–£150 | GGF member pricing survey 2026 |
| Replacement cost per window (typical range) | £200–£500 | Checkatrade average cost data 2026 |
| Annual energy saving after repair (estimated) | £20–£40 per window | DESNZ home energy efficiency statistics (DESNZ, 2026) |
| U-value of repaired window (if unit replaced) | 1.2–1.6 W/m²K | EST window U-value database (Energy Saving Trust, 2026) |
| U-value of original window (pre-repair) | 2.0–2.8 W/m²K (with failed seal) | EST window U-value database |
A repaired window with a new sealed unit restores its original U-value, typically 1.2 to 1.6 W/m²K for modern double glazing. The Department for Energy Security and Net Zero (DESNZ) estimates that repairing a failed seal saves around £20 to £40 per window annually in heating costs (DESNZ, 2026).
Who pays for failed double glazing repair? Grants and eligibility
No government grant covers the repair of existing failed double glazing. Grants are only available for new installations or whole-home upgrades. The Great British Insulation Scheme (GBIS) does not cover window repair; it focuses on loft and cavity wall insulation (GOV.UK GBIS eligibility page, 2026).
The Energy Company Obligation (ECO4) may fund window replacement, but only if the home has no central heating and the windows are single-glazed. It does not cover repair of double glazing (Ofgem ECO4 guidance, 2026).
Homeowners must pay for repair themselves. Landlords are responsible for repair in rental properties, as the failure affects the property’s energy efficiency and habitability.
How to verify your installer for failed double glazing repair
To ensure the work is done correctly and comes with a guarantee, your installer must be registered with a competent persons scheme. For windows, the two main schemes are FENSA and CERTASS. Check the installer’s FENSA registration number on the FENSA website before hiring (FENSA register, 2026).
TrustMark accreditation is also recommended for consumer protection. TrustMark is a government-endorsed quality scheme that covers all home improvement work (TrustMark website, 2026). Always get at least two quotes and ask for a written guarantee on the repair.
Failed double glazing repair the direct answer for homeowners
The most common and cost-effective fix is to replace the sealed unit only, not the entire window. This repair is typically done by a FENSA-registered glazier and costs £80 to £120 per standard window in 2026. The GGF technical guidance confirms that replacing the sealed unit restores thermal performance and eliminates condensation between panes (GGF technical guidance, 2026).
However, repair does not improve U-values beyond the original window’s rating. If your windows are very old and the frames are in poor condition, full replacement may be a better long-term investment. double glazing replacement vs repair cost comparison
When replacement is the only option for failed double glazing
Replacement is necessary if the frame is rotten, damaged, or single-glazed. Windows installed before 2002 may have non-replaceable sealed units due to obsolete manufacturing standards. The GGF advises that if the frame is in good condition, the sealed unit can be replaced; if not, the whole window must go (GGF advice on obsolete units, 2026).
If your home is a listed building or in a conservation area, replacement may require planning permission. Historic England guidance states that repair of existing windows is usually permitted, but full replacement may need consent (Historic England guidance on windows in listed buildings, 2026). Always check with your local planning authority before proceeding. listed building window replacement rules
Frequently Asked Questions
Repairing a failed double glazing seal costs between £80 and £120 per window in 2026, according to the Glass and Glazing Federation. Full window replacement would cost £200 to £500 per window.
Yes, in most cases you can repair the seal without replacing the whole window. The Glass and Glazing Federation confirms that replacing just the sealed unit is often possible, leaving the frame intact.
The clearest sign is condensation between the glass panes that you cannot wipe off, appearing as mist or fog. The Energy Saving Trust says this means moisture-laden air has entered the gap due to a failed seal.
Repairing the seal is almost always worth it, costing £80-£120 per window compared to £200-£500 for full replacement. GOV.UK advises that repairing the sealed unit is more cost-effective unless the frame is damaged.
A properly repaired double glazing seal can last 10 to 15 years, similar to a new sealed unit. The Glass and Glazing Federation recommends using a certified installer to ensure long-lasting results.
