[derekgas]

I have spoken to Flashy, there used to be a back boiler in the room, in which case it could be life threatening to block the vent up, as the replacement boiler was installed into the kitchen, and the current fire is less than 7 kw input, then in this instance it is safe to block up the vent, I am most impressed that Flashy had the sense to ask the question prior to blocking the vent, I happen upon blocked vents fairly regularly, and it is usually because the owners are experiencing nausea or the appliances are not working properly! If you have a vent in a room with a gas appliance please, for your own safety, DO NOT cover it up without taking advice from someone who is QUALIFIED to give that advice.
Trickle vents in windows are NOT to aid the burning of fossil fuels in appliances or grates, but to help prevent condensation.