I'm having a major problem with water hammer in our heating pipes. I to open the drain on the lines to flush out the air which I was told would cause this... After doing this for 30 min or so, I noticed less and less air coming through. Eventually it looked like air had stopped, and a test seems to prove that the water hammer is stopped as well. Now comes the issue... After about 1 day, the water hammer comes back in full force... I can understand a week or two this could happen, but I don't see how after 1 day I could get such a level of air in the pipes to cause the banging...


Anyone have any ideas on where I can check to see what is causing this? :confused:

This is not a plumbing issue but rather an hydronic issue.

Home Improvement: Maintenance: What is Water Hammer?
[from the site]... Another source of water hammer occurs in steam heating systems. If the system design allows for water to stand or pond within the steam pipes or radiators, then you hear that "bang" when the thermostat calls for heat from the boiler.

This occurs because the accumulated liquid water is cooler than the steam. When the steam passes over condensed water in the line that has not drained back to the boiler correctly, it cools, condenses, and suddenly shrinks to 1/1,700th the volume it filled as steam. That leaves a vacuum directly above the water. The water leaps up to fill the vacuum and crashes into the pipe, Clang! Bang!. water hammer.
See also Water hammer - Wikipedia, the free encyclopedia
And this is probably your best hope Home Heating Systems Newsletter - HeatingHelp.com

Unfortunately this is not a steam systen... its hot water system. All the instructions o've seen for the hot water system include opening the drain on the end (which I have tried).

I have very little experience on hot water home heating but a water hammer is still a water hammer. Both the plumbing side and the steam side suggest an expansion tank. I would try that first. Possibly someone else in here could better address this problem.

Both Doug and I are Southern plumbers without a lot of heating experience but his suggestion of adding a expansion tank as a air chamber, (shock absorber) sounds like a winner to me. Regards, Tom

Hot water systems are normally built with an expansion tank just above the boiler. Have you drained the expansion tank too?

I've drained the entire system, but I'm not sure if that will drain the expansion tank as well...

I'm considering putting in a shock absorber for each of the zones... but I still have concerns that this much air is making it into the lines...

Anyone have recommendations for where to put the shock absorbers? Any specific distance from the zone valve? Or should they be on the opposite end from the zone valve?

I am going to have to bow out of this one. If I remember correctly there is a device that purges air out of your system. Is your boiler set too high? Turn it down.