I have a heating system, powered by LPG which whilst very quiet most of the time, I have a problem with banging rads. The piping is micro pipe and each rad has a TRV with both the inlet and outlet on the same end, therefore no lockshield valves to adjust. When I get a banging rad, adjusting the TRV gets rid of the noise. I have drained the system down and re-filled it once, which made no difference. Any ideas would me most gratefully received