Trickle Ventilators

We have a load of trouble this past winter season with trickle ventilators being draughty when closed! I would not be unreasonable to think that when closed trickle ventilators don’t let in draughts. BUT A LOT OF THE TIME THEY DO! 

Here are two both less than ten years old and both draughty, note the dust staining. The first one had never been opened, the householder didn’t even know what it was! 

Dark stains are dust left behind as draughts enter when the TV is closed!

          The above vent from further back. 

Leaky trickle ventilator, the window was also slightly draughty between the over the head ventilator and the frame.