The WindowMaster WML 825 is a chain drive that is installed concealed in VELUX roof windows. If it is faulty, you can keep opening the window electrically with a chain drive from Vent Systems – with a matching bracket for VELUX centre-pivot windows.
WindowMaster WML 825 and Vent Systems alternative compared
| Feature | WindowMaster WML 825 | Alternative from Vent Systems |
|---|---|---|
| Voltage | 24 V DC | VS-KA: 24 V or 230 V |
| Suitable windows | VELUX GGL and GGU from size F06, VL from size 033 | VELUX centre-pivot windows with matching bracket |
| Installation | concealed, integrated in the window | visibly mounted on the frame |
| Force | Locking force 3000 N | VS-KA: 250, 400 or 600 N thrust |
| Stroke | not stated on the manufacturer’s website | VS-KA: 100–450 mm |
| steering | WindowMaster control units WSC 3xx and WSC 5xx | 24 V: ventilation or SHEV control unit · 230 V: directly on a switch |
Which drive fits?
- Existing 24 V cable and control unit: VS-KA in 24 V. We will check, based on the control unit type, whether it can be operated on your existing WindowMaster control unit.
- Ventilation only, without control unit: VS-KA in 230 V, operated via a switch. The 230 V connection is installed by an electrician.
- Force and stroke: For standard centre-pivot windows, the VS-KA with 400 N is usually sufficient. Choose the stroke according to the desired opening width.
What to consider when replacing a drive
- Appearance: The WML 825 sits concealed in the window, the VS-KA is mounted visibly on the frame.
- Window type and size: When enquiring, state the VELUX type and size from the type plate so that the bracket fits.
- Instructions: More about VELUX windows with chain drives in our guide Chain actuator for roof windows.
Important for SHEV: If the window is part of a tested natural smoke and heat exhaust ventilator (NSHEV), the drive may only be replaced by a type named in the test or declaration of performance of the NSHEV. If in doubt, ask your SHEV specialist or us.
Photograph the type plate – we will name the right drive
Send us a photo of the type plate and the window via WhatsApp to +49 176 57801935 or call us: +49 40 50694631 (Mon–Fri 8 am–5 pm). You will receive a specific recommendation with price – stock items shipped from Hamburg within 24 hours.
All WindowMaster drives at a glance: Replacing WindowMaster actuators. All manufacturers in one list: replacement table for window drives (PDF)
WindowMaster and WML 825 are trademarks or product names of WindowMaster International A/S, VELUX is a trademark of the VELUX Group. Vent Systems is not affiliated with these manufacturers. The manufacturer data comes from publicly available product information (as of October 2026) and is for technical comparison only. Please check dimensions and values on the existing drive before replacing it.
Frequently asked questions
Which actuator replaces the WindowMaster WML 825?
As an alternative from Vent Systems, the VS-KA chain actuator with a bracket for VELUX centre-pivot windows fits. For typical centre-pivot windows, the VS-KA with 400 N is usually sufficient.
Does the replacement run on my WindowMaster control panel?
We check whether the VS-KA in 24 V can be operated on your existing control panel based on the panel type. Without a control panel, use the VS-KA in 230 V on a switch.
Does the replacement look different from the WML 825?
Yes. The WML 825 is concealed in the window, while the VS-KA is mounted visibly on the frame. Tell us the window type and size so we can select the right bracket.
Note: The brand and product names mentioned belong to their respective owners. They are used here only to indicate technical compatibility. Vent Systems is not affiliated with these manufacturers; only Vent Systems’ own actuators are offered.
In brief: As an alternative to the WindowMaster WML 825 in VELUX roof windows, Vent Systems offers the VS-KA chain actuator with a suitable bracket for VELUX centre-pivot windows. For typical centre-pivot windows the VS-KA with 400 N is usually sufficient, in 24 V on a control unit or in 230 V on a switch. Unlike the WML 825, the VS-KA is mounted visibly on the frame.