Changed our minds about the rayburn base. We put the unit into place, and it has to come out from the fireplace a bit. Dont really want a step coming out into the room, so are going over to the idea of tiling the whole floor (inc the fireplace) and then getting a lump of slate for the rayburn to sit on.
I did manage to re-install the biodiesel boiler on sunday though, and then make a 200 ltr batch of fuel heated from the other boiler. It was after 1am by the time i got it onto demeth, and went to bed... (to get up at 6:45 the next morning) - so i havent been slacking!