I recently replaced 4 rads in my system, at the same time I treated the system with sludge remover. However, one of my rads is still stone cold. I have standard valves, I have checked for an air blockage, and I have now removed the rad in question to check the water pressure at the valves to find the feed pipe is fine but the outlet trickled with the occassional black chuck of corrosion. I have a microbore system which I assume is blocked up as could be; is there anyway of removing the blockage without an expensive plumber?