There really isn't much to go wrong with them, and since you say that both don't work, it's very unlikely that both have failed at the same time. It might be an adjustment problem, such as previous owners having disabled them for winter. I assume you've found the black cylinder that tony mentioned, so start with the roof vent and screw it clockwise looking from the 'blank' end until the window starts to open. If it's warm and sunny keep screwing till the window is about half way open; if it's dull or cool, less so. After that it needs you to keep an eye on its behaviour. If the window moves at all as the inside temperature changes then all is well, and after a few days you will have found a setting to suit you, by scewing in or out to make sure the window closes before it gets too cold. Once you've got that sorted, try to synchronise the louvre vent with it in the same way, so they both open at the same time, and forever after that they'll take care of themselves. From memory, mine start to open at about 25-30º (75-85)
Geoff.
