pipes knocking

gidget

I have a old house with steam heating.  Recently the automatic feed flooded and water came out of all the  radiator valves. Now when the steam comes up there is a terrible knocking in the pipes.  It sounds like a demolition crew is working.  What can I do?

Jamie Hall

Earplugs?

More seriously.  First question -- how recently is recently?  If it was very recently -- like today -- it may go away by itself.  It does happen.  Rarely.



Most likely, what has happened is that water has gotten trapped in places it shouldn't be.  The first thing to do is to make sure that the water level in the boiler is back where it should be (and find out why the automatic feeder flooded, of course).  In principle, the water should drain back by itself to the boiler.  However, in a flooded system, it may be that there are low places -- sags -- in pipes which don't normally give trouble, but have trapped enough water now to hammer.  Another possibility is that the radiator vents may have been damaged; sadly, that is quite possible.  If so, one or more of them may not be opening, and water may be trapped in the radiator -- which will bang when steam tries to get into the same radiator.



There are other possibilities.



One thing to start with is to try to localise the banging.  While such bangs do telegraph in pipes, and can often be heard at quite a distance from where they are really happening, it is equally often possible to locate one or more places which are the source of the trouble.  Then you can look at those for places or ways water may have gotten trapped.