Rick
The noise is because live steam is hitting condensate (water). This indicates one or more bad steam traps. You probably have steam traps on each register. They are intended to open when condensate hits them (to allow the condensate to return to the boiler), and close when the condensate has emptied, and steam is present.
You may be able to tell the most likely steam traps to replace by either the register with the most noise, or feeling the condensate return piping on the register side of the trap. If the piping is not really hot, it means condensate is sitting in the pipe, and the trap is not opening.
The two most common types of steam trap are the inverted bucket trap
and the thermal disc trap
Either of these work pretty good.
If you try to replace the bad traps yourself, make sure you shut off the heating system and allow it to cool – steam and hot water both cause serious burns. It might be best left to a professional.
Good Luck,
Rick
[Edited by Rick on 26 January 2001]
