Hi again. Exploring options for my bro's flat. One is to convert to a pressurised system. The preferred location for the new unvented cylinder would be where the current vented one is in his airing cupboard. Problem is, it would be tricky to get a gravity drain from this to the outside (he had to have his new boiler fitted in the roof hut for a similar reason to do with the condensate drain). I know there's pumps and stuff, but that's pants. Do unvented cylinders require a 'gravity' drain like this, or have I misunderstood (I'm guessing it's to do with the tundish thingy?)? If it is required, are there any solutions that don't require 'gravity'?! Thanks again.