Velux and other roof windows are exposed to weather on all four sides, making them one of the more demanding components in a house to keep watertight and operational. When problems develop — a drip during rain, a handle that will not move, or fog between the panes — it helps to understand what is actually failing before calling a contractor, as the diagnosis dramatically affects both the cost and who you need to call.
The majority of reported “Velux leaks” turn out not to be Velux problems at all — they are flashing failures that would affect any roof window. Knowing the difference saves wasted call-outs.
Common Velux Problems and Their Causes
1. Water Leaking In During Rain
Water entry during rain is the most alarming and most misdiagnosed Velux problem. There are four distinct failure points, each with different repair approaches:
Lead flashing failure — the most common cause. The soaker flashing and apron that direct rainwater away from the frame-to-roof joint can lift, crack, or have their sealant harden over time. Water tracks under the flashing and appears at the ceiling. This is a roofing problem, not a Velux problem; a roofer (not a glazier) should attend.
Compression seal failure — the rubber seal where the sash meets the frame degrades and no longer compresses watertight when the window is closed. Water enters around the frame perimeter rather than from the roof. The window may also feel slightly easier to open than it used to.
Draught seal (brush pile) collapse — less likely to cause active ingress on its own but can allow windblown rain to enter around the sash in stormy conditions.
Cracked or broken flashings around electrical cable entries (on electric and solar models) — a minor but frequently overlooked source of localised drips.
Diagnosis: In dry weather, run a garden hose along each edge of the window in turn, sealing one edge at a time with a towel to localise where water enters. This simple test distinguishes flashing from frame seal failure in minutes.
2. Condensation Between the Glass Panes
Fog or droplets trapped between the two glass panes means the hermetic seal of the double-glazed unit has failed, allowing moist air to enter the cavity. Once the seal has gone, it cannot be repaired — the entire glazing unit must be replaced.
This is a supply-and-fit job requiring the unit to be ordered to the exact Velux model and glass specification. Replacement units are available with various glass options including anti-glare, solar control, and acoustic variants.
3. Stiff or Broken Handle / Locking Mechanism
The centre-pivot handle and locking mechanism on older Velux windows is the most frequently replaced spare part. Causes include:
- Hardened lubricant on the winding gear or handle linkage — often resolved by a thorough clean and regrease without part replacement.
- Broken handle — the lever or casting cracks, typically from overtightening against a warped frame or from a sharp impact.
- Seized locking pins — the side pins that locate the sash in the closed position corrode and stick, making the window impossible to open or lock properly.
Most handle assemblies are model-specific but are stocked by Velux directly (velux.co.uk/spare-parts) and by independent suppliers. Some discontinued models have been superseded by updated handle designs that are cross-compatible.
4. Broken or Bent Hinge/Pivot
The top pivot hinge on a centre-pivot Velux is a heavy-duty component that rarely fails in itself, but the connecting rod and end links can bend or snap if the window is forced open against an obstruction, or if the winding mechanism is operated with the window frozen shut.
5. Electric Model Not Responding
For electric and solar-powered Velux (INTEGRA range), common failures include:
- Drained solar battery (after extended cloudy periods)
- Faulty rain sensor
- Lost pairing between remote and actuator
- Actuator motor failure
Most of these are resolvable without hardware replacement by resetting the control unit per the installation manual. Actuator replacement (if the motor has failed) costs £120–£250 in parts alone.
Repair Costs (UK, 2026)
| Problem | DIY possible? | Professional repair cost |
|---|---|---|
| Lead flashing re-seal or patch | Possible but risky at height | £150–£350 (roofer) |
| Full flashing replacement | No | £350–£700 (roofer, includes materials) |
| Compression seal replacement | Yes (with correct seal) | £80–£160 per window |
| Glazing unit replacement | No — requires specialist | £150–£350 per unit supply + £80–£150 fit |
| Handle replacement | Yes | £25–£60 parts; £50–£120 with labour |
| Hinge / connecting rod replacement | Possible with manual | £40–£120 parts; £80–£180 with labour |
| Electric actuator replacement | No | £120–£250 parts + £80–£150 labour |
| Full window replacement (supply and fit) | No | £500–£1,200+ |
When to Repair vs Replace
| Factor | Repair | Replace |
|---|---|---|
| Window age | Under 20 years | Over 25 years |
| Number of faults | Single isolated fault | Multiple concurrent problems |
| Glazing condition | Seal intact, clear glass | Condensation between panes |
| Frame condition | Sound, no rot | Rotting timber, bent frame |
| Parts availability | Stocked or easily sourced | Discontinued, long lead time |
| Cost of repair vs replacement | Under 50% of replacement cost | Over 50% of replacement cost |
A Velux window installed in the 1990s that presents simultaneously with a failed glazing unit, a broken handle, and compromised flashing is almost certainly cheaper to replace than to repair piece by piece — particularly when scaffold or roof access costs are factored in.
Finding a Velux Repairer
Velux has an official installer and service network searchable via their UK website. However, independent roofers who are familiar with Velux products are generally equally competent for flashing repairs and often charge less. For internal mechanical or glazing repairs, specialist roof window contractors (search “roof window specialist” or “Velux repair [your town]”) are the most efficient option.
Get at least two quotes for any repair over £200. A competent contractor should be able to diagnose the problem visually before quoting, and should specify which parts are needed rather than giving a vague estimate.
Always ask whether the repair comes with a guarantee against recurrence — a quality flashing repair should carry at least a 12-month guarantee against further ingress.
