the central heating system is a powermax 155x.sealed unit. when running the rads are red hot in the home.the pressure holds at 1.5 bar,no problem.But since they have had a single storey extension done the two rads in the extension(0.900x0.600) got hot when first turned on by the plumber and then stopped working.I can get heat to the rads if i drain off the system from the 2 rads and pull the hot water throw to the rads,but as soon as i close the rads up the rads lose their heat.I have closed all rads down upstairs to push the heat down stairs the rads get hot but not as hot as the other rads and when i turn the rads back on up stairs the 2 rads in the extension loose there heat.The two rads in the extension are connected to the system by 15mm plastic pipe at the upstairs bedroom rads
help needed,
terry
help needed,
terry