How to Engage and Dis-engage a VELUX Top Hung Window

Posted by Alice King on 9th April 2021

Engaging and dis-engaging the spring for VELUX Top Hung windows can be challenging. This blog will help explain in detail how to handle this operation correctly and appropriately, ensuring your installation goes smoothly.  

Engaging the spring

After installing your VELUX Top Hung window, you need to engage the spring so the window sits and functions correctly. 

Firstly pull the window to its full extent and listen out for two large clicks of the springs engaging. From this the window is free to operate in its normal top hung function. 

You must then check that the window is suitable for the roof pitch. In order to do this you need to make small adjustments to the spring tensions on both sides.

Automatically the plate is positioned to suit the upper range of the natural roof pitches of the window. Therefore anything from 45-55 degrees, you wont need to adjust the spring tension. For roof pitches less than 45 degrees will require adjustments so it can be operational. 

To adjust find the small plate on either side, just inside the channel which you can access yourself onsite. Inside the internal finish you should see the different settings for the tensions on the spring system that runs inside the window.

Find the tab that you need to move lower down to suit lower roof pitches, e.g. for 15 degree pitch you would need to move the tab to the very lowest element. 

To move the tab, find the small slot on the tab and with a slotted screwdriver, elevate it up and use your fingers to slide it down and drop it into any position that is required. Repeat on the opposite side so the tension is the same.

Choosing the wrong tension will mean that when closing the window it will want to open by itself. Rule of thumb, if the window lifts upward then you need to move the adjustment plate up. If the window creeps down, then you need to move the tension plate down. This may require adjusting when features like blinds are added because of the extra weight they provide.

Dis-engaging the spring 

Dis-engaging the spring mechanism is required in case you have accidentally engaged the springs right at the beginning and we want to drop these arms to get the sash inside OR if you're doing any maintenance work and you have to remove the glazing unit or the sash itself.

Your key focal point is the large fixed plate, just above the adjustment plate.

Take a slotted screwdriver or similar, come in at an angle and rest just on top of the plate. By coming in at an angle the screwdriver is going to rest underneath a small return on the mental frame, so its now meeting a little resistance.


Make sure you've got hold of the window because you are now going to disengage the springs. 

Pull down on the screwdriver handle so it levers the section up, separating the two sections. Listen out for the clunk as the springs separate.

You should now be able to see the nodule in the corner which is what engages into the fixed element to make the springs lock together. 

While holding the weight of the window repeat the action on the opposite side. You will suddenly feel the whole weight of the window on your arm. 

Slowly lower the window down, and let go of the window at the same time. You will realise that the spring isn't engaged as it becomes a dead weight.

After finishing your work to re-engage the spring, push the window open until you hear the springs click and everything is back to fully functioning VELUX Top Hung window. 

View the VELUX installation video here.