Many thanks to those who responded to the previous thread, still got problems though...
I refilled the Saunier Duvall boiler, closed off the filling and failsafe valves, and bled the radiators again. The central heating pressure gauge on the boiler is now hovering just a shade above the 1 mark.
I think there's some sort of pressure problem though, the water doesn't seem to be getting moved around the system. The radiator nearest the boiler gets up a lukewarm temperature, I can feel a slight warmth from two others, and the radiators furthest away from the boiler are stone cold. Unfortunately these two are the living room and bedroom :( When I bled the radiators a trickle of water oozed out, every other time I've done it there's always been a bit more pressure and the water would jet out with about the same force as a squirt from a water pistol. The boiler itself is acting wierd. It's too quiet, there used to be a rhythmic sound to it, hard to describe, but you could tell it was working, now it's silent most of the time. The burners don't ignite for long either,
5 to 10 seconds every 15 minutes or so. I've tried all the settings I can think of, from the summertime hot-water only all the way to get-me-through-the-nuclear-winter full monty. Nothing :( On max settings the temperature gauge rises to around 50 degrees C, when it was working it used to get up to 70 degrees.Is there anything more I can try ?