Right apologies for the long post but i think the more information i give the better it'll be.
I'm putting in a new bathroom suite and have exchanged the radiator for a new one, the radiator that is in the bathroom is connected but has the valves closed until i plaster behind it as i will need to remove it.
Yesterday i put the central heating on and the temperature rose to about 70C but then dropped to down to zero and stayed there even though the boiler was still running. I turned the boiler off and bled all the radiators (there was quite a lot of trapped air) i then fired up the central heating last night and it was working fine (agood 3-4hrs) i left it running over night when i awoke this morning all the radiators were cold again but the boiler was still running.
Today while i was washing the dishes (using hot water) i noticed the boiler made a noise so checked on it, the temperature was low but when i shut the hot water off the temperature for the CH started to rise (although only a little) then it dropped back down to zero again
Any help/advice appreciated