Water Hammer in return line

JimmyNJ

Hello all:

I am hoping that someone can help me figure out a strange water hammering problem I am experiencing. I don't have water hammering in my radiators or in the steam mains or supply pipes - rather, I get weird noises (almost sound mechanical) in the return pipe close to the boiler and then heavy water hammering there. It does not happen every heating cycle, just sometimes and I am wondering if it is related to how much water is in the boiler or if something else is amiss. The hammering seems to start at the end of the heating cycle and I have attached a few pics that shows the boiler piping and also the return line (I have verified that the return line has the proper pitch to allow the water to reach the boiler. One of the return lines is a short run (maybe about 12 feet) from the boiler and runs down to a T fitting where it is joined by a much longer return (from the other steam main). I have insulated the short return....is it possible that steam is traveling down that pipe (I didn't think it would b possible for steam to travel downwards) and hitting the condensate from the longer return and creating water hammering? But wouldn't the problem happen every heating cycle if that was the case? Another theory that I may have done something to the system one time earlier this season when i was skimming the boiler, I had forgotten to completely close the ball valve to the water line so the whole boiler filled with water and water may have backed up in the dry return piping - I drained the boiler back to the normal level when I discovered my error (the same day - and the boiler was never firing during that time....but I actually think this new water hammering started soon thereafter so maybe it's related. If someone has any ideas on what could be causing the problem I would great appreciate to hear them. I have circled the one picture on the return line where it appears that the hammering is happening - as you can see it is only a foot or so before the T in the return line...seems to be weird spot.

Jimmy

Fred

How far below the Normal water level is this return? When the water hammer starts, Does the hammer start only on longer run cycles? Is it possible that return is above the boiler waterline after the boiler has made steam for a while and the water level in the boiler has dropped a bit? If so, possibly steam is getting into that wet return.

JimmyNJ

This return pipe is pretty close to the water line, but it does then connect via a T fitting into the other return line and from the T goes vertically down to less than an 1" from the basement floor (so well below the water line) See attached pic where I have indicated where this return line connects with the other pipe.

Fred

All wet returns should tie together below the water line. My guiess is that as the water level drops in the boiler from making steam, that return is then above the water line and getting steam.
When was this boiler installed? I suspect the old boiler had a higher water level and this was not a problem.

JimmyNJ

approved plumbing permit sticker on the boiler is dated 2003. I think you are right because now that you mention it, I believe the clanking has only happened when the water level is mid-level in the sight-glass (when cold) - I added more water this morning and it ran without any hammering on its first heating cycle afterwards. So you think the solution would be to get that other return to connected to the second return (vertical pipe) below the water line in the boiler?

KC_Jones

Also you mention about steam going down. Steam doesn't care which way the pipes run, if it is open steam will go there. So it is entirely possible for steam to be getting into that pipe. Another thought as to why all of the sudden. You could have inadvertently flushed some crud out of those return lines when you overfilled the system. This would have opened the pipe up some more giving room for this problem to rear it's ugly head. As Fred said those pipes really shouldn't come together until they are well below the water line. In your case this would be that copper pipe down at the floor level. Even doing that might not correct the problem. That return I suspect has a slight slop over it's length and ends up at that height? If so that could continue to be an issue. The pipe is "confused" as to whether it's a wet or dry return. You usually see the pipes having a distinct change and crossing through the water line in the vertical in your case it's more in the horizontal so you end up with a situation of a section of pipe that can stay partially filled with water and the steam will take that and hammer it. Again just a theory based on your pictures and what you said.

Fred

Yes, if you can take that return out of that elbow and drop it down further into the copper, even to the bottom, you should be good. You can then just put a plug in the Tee and maybe use that spot if you ever want to flush out the wet return.

JimmyNJ

Fred - just to confirm, you are referring to the moving the horizontal pipe that goes along the wall and into the T and not the "higher" return that is shown in the first picture (with some insulation on it) before it drops down vertically and connects with the horizontal pipe correct? Should I maybe also remove the insulation on the shorter return piping so that it has a better chance of turning into water vs. chance of the pipe still carrying steam (which then could hit the condensate in that horizontal return that goes along the basement wall?) The attached pic shows the "short" return piping.

Fred

Yes, I'm talking about the horizontal line that runs along the wall and ties into the vertical pipe a couple or 3 feet above the floor and behind the water heater. If you drop that, I feel confident that steam won't be able to get into that horizontal line as it will be filled with condensate, up to the Normal water line in the boiler and air in the rest of the pipe will prevent steam from entering that pipe.
The insulation on the other return is fine. No problem

JimmyNJ

Thanks Fred. I will look to get my plumber to fix that.

JimmyNJ

Follow question: If I have that work done, should I also at that time replace the copper piping with black steel? Or is the copper okay on that part of the system? The boiler risers, equilizer, header and system riser is also copper....no clue why someone put copper on these parts when the rest of the piping is all steel.

KC_Jones

Steam carrying lines should always be steel/iron. The wet returns are okay to be copper. So I wouldn't change the ones you are looking to have repiped, but would think about having the other redone at some point. Copper is not good on steam systems.

Fred

The boiler risers, equalizer and Header and system risers should all be black threaded iron pipe. Anything below the water line can remain copper with no problem.

JimmyNJ

Thanks guys - Will look to have those sections replaced at the same time I do the return line work. Appreciate all the pointers/help!

Snowmelt

Jim may I ask where are you from in nj

JimmyNJ

Sure - the beautiful town of Chatham

Fred

Make sure when the plumber replaces the risers off of the boiler that he keeps that skim port on the right side of the boiler (That has a plug in it) Once the new piping has been introduced into the system (even the correction of the return) the boiler will need to be skimmed a week or two afterwards to get the oils from the new piping off of the surface of the boiler water.

JimmyNJ

Yes! I have used it several times already as I had a ton of surging after adding a couple of radiators to the system last year. Very glad that someone put that in there (per Utica instructions) but still not clear why they used copper where they did - maybe because it was "faster" to solder than using black iron pieces?

KC_Jones

Well if you do have the copper replaced at least the recycle value will help offset the cost!

Fred

I'm sure whoever put that copper in either didn't know any better or didn't have the equipment to cut and thread iron pipe so they did what they thought was the next best thing. The only problem is one of these days those solder joints will give out from expansion/contraction.

JimmyNJ

KC - Going back to your comment " That return I suspect has a slight slop over it's length and ends up at that height? If so that could continue to be an issue. The pipe is "confused" as to whether it's a wet or dry return. You usually see the pipes having a distinct change and crossing "

That return pipe does make about a 3 foot vertical drop from the Steam Main and then travels horizontally across the basement wall on a slight slope towards the boiler. You can actually see more of the pipe in the last picture I posted (it is the pipe right by the sponge sitting on the slop sink next to the dryer), but as noted by you and Fred - the problem is that the piping is to high on the wall in relation to the water level of the boiler. Hoping that Fred's suggested fix of taking the current piping out of that T and dropping it down to the bottom of the copper pipe will work.

Fred

It will resolve the problem. I'm sure.

KC_Jones

I think Fred may have hit the nail on the head with the water level. If that pipe was run today as new it would probably have been run at the floor level or up high as a dry return, but with the old tall high water content boilers it was probably well below the water line. I had the same piping arrangement on my system originally. I used the boiler replacement as an excuse to rerun that particular line.

JimmyNJ

Finally got plumber out to re-pipe the section of return piping that was experiencing the water hammering -- after bringing that return below the water line the water hammering has stopped. Thanks for everyone's help and advise!!

Fred

I'm glad that reolved your problem!