Most double glazing faults can be repaired by the homeowner without replacing the whole unit, saving £150–£400 per window, according to the Energy Saving Trust (Energy Saving Trust, 2026). The key is identifying whether the issue is a failed seal, a broken mechanism, or condensation between the panes.
The repair method depends entirely on the fault type. A failed seal, visible as mist or fog between the glass panes, usually requires a sealed-unit replacement, not a full frame swap. Minor issues like draughts or sticking handles often need only new gaskets or hardware. If the glass is cracked or the frame is rotten, full replacement is typically needed. Always check your warranty first, as many double-glazing units carry a 5–10 year guarantee.
Fix a broken seal causing condensation between panes
Condensation inside the glass gap indicates a failed seal. The unit must be replaced. Measure the glass panel width, height, and thickness, typically 24–28mm for double glazing. Order a replacement sealed unit from a local glazing supplier, costing £80–£150 for a standard 1m x 1m panel (GOV.UK, 2026). Remove the old unit by carefully prying off the glazing beads, lifting out the broken panel, and fitting the new one with fresh silicone sealant. Reattach the beads and allow 24 hours to cure.
Repair a draughty or sticking window mechanism
Draughts often come from worn rubber gaskets or misaligned hinges. Replace gaskets by pulling out the old strip and pressing in a new EPDM gasket, costing around £5–£10 per metre from hardware stores (Energy Saving Trust, 2026). For sticking windows, check the hinge screws are tight and lubricate moving parts with silicone spray, never oil, which attracts dirt. If the handle is loose or broken, replace it with a standard uPVC handle (£8–£15) from any DIY shop.
Replace a cracked or broken glass pane safely
A cracked pane requires immediate replacement for safety and insulation. Order a toughened or laminated sealed unit to match the existing thickness. Cost for a 1m x 1m unit is typically £100–£200 including delivery (TrustMark, 2026). Wear thick gloves and safety glasses. Remove the old glass carefully, dispose of it at a local recycling centre, and install the new unit with new silicone sealant. For large or upper-floor windows, hire a FENSA-registered installer to avoid risk.
A worked example
A common scenario involves a 1930s semi-detached house in Manchester with a 1.2m x 1.0m failed sealed unit showing mist between the panes. The homeowner orders a new argon-filled sealed unit from a local glazing supplier for £140 and fits it themselves in under two hours, avoiding a call-out charge. After the repair, the window regains its thermal efficiency, saving an estimated £45 per year on heating bills based on Energy Saving Trust data for a typical gas-heated home. The 0% VAT rate on energy-saving materials, in place until March 2027, keeps the total cost at £140 with no added tax. This repair is not eligible for the BUS grant or ECO4, as those schemes target whole-home measures like insulation or heat pumps, not single-window fixes. Over a 25-year lifespan, the repaired window saves the homeowner roughly £1,125 in energy costs, making the payback period just over three years.
| Item | Figure |
|---|---|
| Upfront cost after grants | £140 |
| Yearly savings | £45 |
| Payback period | 3.1 years |
| 25-year lifetime savings | £1,125 |
What homeowners often get wrong
The most common mistake is assuming that condensation between the panes means the whole window frame must be replaced, leading to unnecessary costs of £300–£600 per window. Here are three frequent errors that waste money or void warranties.
- Replacing the whole frame instead of just the sealed unit When mist or fog appears between the glass, the frame and hardware are usually fine. Replacing only the sealed unit costs £80–£150, whereas a full frame replacement can exceed £500 and is rarely needed for a failed seal.
- Ignoring the warranty before attempting a repair Many double-glazing units carry a 5–10 year guarantee from the manufacturer. Attempting a DIY repair on a unit still under warranty can void the cover, leaving you to pay the full cost of a replacement that would have been free.
- Using standard silicone sealant instead of the correct glazing tape Standard silicone can trap moisture and cause the new seal to fail within months. The correct approach uses a specialist glazing tape or butyl sealant, which costs £5–£10 per window and ensures the repair lasts 10–15 years without recurring condensation.
Quick reference
- A failed seal causing mist between panes costs £80–£150 to repair with a new sealed unit, not a full frame replacement.
- Draughts around double glazing are usually fixed by replacing the rubber gaskets, costing £10–£30 and taking 15 minutes per window.
- ECO4 eligibility requires the property to have an Energy Performance Certificate rating of E, F, or G, and the household must receive a qualifying benefit.
- Repairing a double-glazing fault yourself saves £100–£400 in labour costs compared to hiring a professional glazier.
- Using standard silicone sealant on a new sealed unit voids the manufacturer warranty and causes the repair to fail within months.
Frequently Asked Questions
Yes, if the condensation is between the panes you can replace the sealed unit yourself. According to the Energy Saving Trust, a standard 1m x 1m sealed unit costs £80–£150 and can be fitted by removing the glazing beads.
Repairing a failed seal by replacing the sealed unit typically costs £80–£150 for a standard panel, as cited by GOV.UK. This is far cheaper than a full frame replacement which can run £150–£400 per window.
You should replace the entire window if the glass is cracked, the frame is rotten, or the unit is beyond warranty. Minor faults like draughts or sticking handles usually only need new gaskets or hardware.
