Double glazing is one of the most valuable thermal upgrades in any UK home, so when something goes wrong it is worth understanding whether repair or replacement is the right call — and what it is likely to cost. The good news is that most common faults are repairable for a fraction of the price of new windows. This guide covers every common failure mode, what causes it, how to fix it, and realistic 2026 UK costs.
The Most Common Double Glazing Problems
1. Misted or Cloudy Glass (Failed Sealed Unit)
The most frequently reported problem is condensation between the two panes — a milky or steamy appearance that cannot be wiped away. This happens when the argon-filled hermetic seal around the edge of the glass unit breaks down, allowing moist air to enter.
Repair option: The glass unit (not the frame) can be replaced. A tradesperson removes the glazing beads, slides out the old unit, and fits a new double or triple glazed unit. This is almost always cheaper than replacing the whole window.
Replacement unit cost: £100–£300 per unit depending on size, glass spec (low-E coating, safety glass, Georgian bar), and accessibility.
Labour: £50–£100 per window for a glazier. Many glaziers carry stock sizes, so a same-day turnaround is often possible.
“Resealing” drilled units: Some companies drill small holes to inject desiccant and clear the misting temporarily. This is not a permanent fix — the seal remains broken — and Renovation Notes does not recommend it.
2. Broken or Stiff Hinges
UPVC and aluminium windows use friction stay hinges (also called egress hinges or casement stays). These wear over time, causing the window to drop, drag on the frame, or fail to stay open. Replacement is straightforward.
Cost: £50–£120 per window including labour. Hinge sets cost £15–£40 in parts; a window repairer charges 30–60 minutes labour.
Safety note: If a bedroom window is fitted with a child safety restrictor, make sure the replacement hinge also accommodates a restrictor pin — this is a requirement under Building Regulations Approved Document K for windows above ground-floor level in dwellings with children.
3. Broken Handles and Locks
UPVC handles break through repeated use, impact, or UV degradation. Multi-point locks (the long strip locking mechanism in the frame) can seize, fail to engage, or snap. Both are common after 10–15 years.
Handles: Usually £20–£60 to replace including parts, DIY-accessible with a screwdriver.
Multi-point locking mechanism: £80–£250 depending on the mechanism brand and whether the lock strip itself needs replacement. This is a specialist job — incorrect fitting can leave a window insecure.
Lock cylinders (euro cylinder): If a key breaks in the lock or a cylinder fails, replacement cylinders cost £20–£60 and swap in 10 minutes. Choose a TS007 3-star or Secured by Design rated cylinder for security compliance.
4. Draughts Around the Frame
Air infiltration around the perimeter of the window usually means the rubber gasket seals inside the frame have perished or the frame itself has warped slightly. Gasket replacement is a low-cost repair; frame warping is harder to address.
Gasket replacement: £30–£80 per window including labour. Gasket material is inexpensive (£5–£20 per window in parts); it is the time tracking down and pressing in the correct profile that costs.
Frame adjustment: Many UPVC windows have adjustable compression hinges and strike plates. A window repairer can adjust these to improve the seal for £40–£80 per call-out.
5. Water Ingress and Leaks
If water enters around the frame rather than through the glass, suspect failed exterior silicone sealant or a blocked drainage channel in the frame. UPVC frames have small drainage slots at the bottom of the outer frame face — these can block with debris and cause pooling.
Fix: Clear the drainage slots with a thin implement and re-apply exterior silicone sealant (Soudal FC or similar, paintable grade if needed). Total cost as DIY: £10–£20 in materials. A tradesperson would charge £40–£80.
Double Glazing Repair Cost Summary
| Problem | DIY cost | Tradesperson cost |
|---|---|---|
| Failed sealed unit (misted glass) | Not recommended | £150–£350 per window |
| Hinge replacement | £20–£50 (parts) | £60–£130 per window |
| Handle replacement | £15–£30 (parts) | £40–£80 per window |
| Multi-point lock mechanism | £60–£120 (parts) | £100–£250 per window |
| Gasket/draught seal | £10–£25 (parts) | £40–£90 per window |
| Exterior silicone re-seal | £10–£20 (materials) | £40–£80 per window |
| Full frame + glass replacement | — | £400–£900 per window |
Repair vs Replace: How to Decide
The rule of thumb in 2026: repair if the frame is sound, replace if the frame is damaged or the window is over 25 years old.
Key questions:
- Is the UPVC discoloured, chalky, or cracked? Repainting is possible but once UPVC cracks structurally, replacement is better value.
- Does the frame fit square? Severe distortion means the building structure has moved — address the cause first, then replace the window.
- Are you on an energy-efficiency improvement programme? If so, replacing single-pane or older double-glazed units with modern A-rated or better windows makes financial sense. Under the ECO4 scheme and the Warm Homes Plan successor programmes in 2026, some households may qualify for funded glazing upgrades through their energy supplier — check gov.uk or call 0800 444 202.
Finding a Reputable Double Glazing Repairer
Double glazing installation and repair is not licensable, but use traders who are:
- FENSA-registered (for unit/frame replacement — triggers a completion certificate)
- CERTASS-registered (alternative self-certification body)
- TrustMark-registered (for funded retrofit work)
For repairs that do not replace the whole frame or unit, FENSA registration is not required, but always get a written quote and check reviews on Checkatrade or Google.
Building Regulations and Double Glazing
Replacing a full window (frame and glass) in England is notifiable under Building Regulations, and installers must either be FENSA/CERTASS registered or you must apply for a Building Control notice. The regulations require:
- Thermal performance: U-value of 1.4 W/m²K or better for the whole window unit (Part L)
- Ventilation: Replacement windows must include a trickle vent if the original window had one, or if the room requires background ventilation (Part F)
- Safety glazing: Any glazing in critical locations (below 800 mm from floor, adjacent to doors) must be safety glass (toughened or laminated) per Part N
Replacing just the glass unit within an existing frame is generally not notifiable. Replacing only hardware (handles, hinges, locks) is never notifiable.
When to Call a Professional
Call a glazier or window repairer rather than attempting DIY when:
- The glass unit has cracked or broken (handling broken toughened glass is hazardous)
- The frame is distorted or out of square
- The multi-point locking mechanism has failed (security implications)
- The window is above ground level (working at height rules apply)
For most hardware repairs — handles, hinges, cylinders — a confident DIYer with basic tools can save £30–£80 per window. The main risk is buying the wrong replacement part: always photograph the existing component and measure before ordering.
