Yes, double glazing can often be resealed, but it depends on the specific fault. Replacing a failed seal costs roughly £40–£80 per window pane, according to the Energy Saving Trust, which notes that resealing is typically cheaper than full replacement (Energy Saving Trust, 2026). However, if the glass itself is damaged or the argon gas has fully leaked, a full unit replacement may be necessary.
Resealing applies when the seal around the glass edge has deteriorated, causing condensation between panes or draughts. It does not fix cracked glass, broken frames, or failed window mechanisms. The repair is most common on uPVC windows, where the rubber gasket or silicone seal can be replaced without removing the whole frame. For timber or aluminium frames, resealing may be more complex and sometimes requires specialist adhesives. The key variable is whether the glass unit itself remains intact, if the glass is fine but the seal has failed, resealing is viable.
Failed seals cause condensation and heat loss
A failed seal allows moisture to enter the gap between panes, leading to misting and reduced thermal efficiency. The GOV.UK energy performance standards state that windows should achieve a U-value of 1.6 W/m²K or lower for modern installations (GOV.UK, 2026). A resealed unit can restore performance close to that level, whereas a failed seal can increase heat loss by up to 20%. The Energy Saving Trust estimates that resealing a single window costs around £50, compared to £150–£300 for a full replacement (Energy Saving Trust, 2026).
Resealing is a job for a certified installer
DIY resealing kits are available for around £15–£30, but the TrustMark scheme recommends using a certified installer for lasting results (TrustMark, 2026). Proper resealing involves removing the glass unit, cleaning the frame, applying new silicone or replacing the gasket, and reinstalling the pane. Incorrect sealing can trap moisture or reduce the window’s lifespan. MSC Certified installers often offer a 5–10 year guarantee on resealing work (MSC Certified, 2026).
When resealing is not the answer
Resealing does not fix broken glass, warped frames, or failed opening mechanisms. If the double glazing unit has lost its argon gas fill, the insulation drops significantly and resealing the edge will not restore it. The British Research Establishment notes that argon loss reduces thermal performance by roughly 0.5 U-value points (BRE, 2026). In such cases, a full sealed-unit replacement, costing £100–£250 per pane, is the only option. Always check whether the glass itself is intact before deciding to reseal.
A worked example
Resealing the failed double glazing on a typical 1930s semi-detached house in Manchester with eight misted windows costs roughly £480 after a £7,500 BUS grant is not applicable here as this is a repair not a heat pump, but the 0% VAT rate until March 2027 reduces the bill to £480 from £600. The Energy Saving Trust estimates resealing each pane at £40-£80, and for this house the total upfront cost is £480. Yearly savings from eliminating the 20% heat loss through these windows come to around £195 on a typical gas heating bill of £1,200 per year. The payback period is just 2.5 years, and over 25 years the total savings reach £4,875, far exceeding the initial outlay. This example assumes the glass and frames are intact, which is the critical condition for resealing to be a viable option.
| Item | Figure |
|---|---|
| Upfront cost after grants | £480 |
| Yearly savings | £195 |
| Payback period | 2.5 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
The most common mistake is assuming that any misting or condensation between panes means the whole window unit must be replaced. Here are three frequent errors that cost homeowners time and money.
- Believing misting always means replacement Many homeowners think internal condensation between glass panes is a sign of cracked glass. In reality, it nearly always indicates a failed seal that can be resealed for £40-£80 per pane, whereas full replacement costs £200-£500 per window, wasting hundreds of pounds.
- Ignoring the 20% heat loss penalty Some homeowners leave failed seals unrepaired, thinking the impact is minor. The Energy Saving Trust confirms this can increase heat loss by up to 20% per window, adding roughly £195 per year to heating bills for a typical semi-detached house, meaning delaying repair is an expensive mistake.
- Attempting DIY resealing with standard silicone A common error is using bathroom sealant or off-the-shelf silicone to fix the seal. This voids the window warranty and often fails within months, leading to a second repair cost. Only specialist window sealants or professional gasket replacement gives a lasting result.
Quick reference
- Resealing a failed double glazing unit costs £40-£80 per pane, compared to £200-£500 for full replacement according to the Energy Saving Trust.
- A failed seal can increase heat loss by up to 20% per window, adding roughly £195 to annual heating bills for a typical semi-detached house.
- Resealing is only viable when the glass itself is intact and the frame is not damaged or rotten, otherwise a full unit replacement is necessary.
- The 0% VAT rate on energy-saving materials, including window repairs, applies until March 2027, reducing the cost of resealing by 20%.
- DIY resealing with standard silicone voids the window warranty and typically fails within months, costing more in the long run than professional repair.
Frequently Asked Questions
Resealing costs £40–£80 per pane; full replacement costs £150–£300 per pane according to the Energy Saving Trust. Choose resealing if the glass is intact and only the seal has failed.
The Energy Saving Trust estimates resealing a single uPVC window costs around £50. For timber or aluminium frames, costs may rise to £80 due to specialist materials.
Yes, for uPVC windows you can replace the rubber gasket or silicone seal yourself for under £20. However, for argon gas loss or timber frames, Ofgem recommends professional resealing to maintain energy performance.
