Steam systems need an experienced team to decipher the problems and know how to fix them. The banging sound could be caused by a steam line which is holding water. The drastic difference in the hot steam and cool water creates a loud, violent, banging noise. It could also be the piping near the boiler (if installed improperly) causing banging elsewhere in the house. Let us monitor the WHOLE system and get to the root of the trouble without hurting your wallet any more than needed. We know steam systems!!!