Excessive Water Hammer / Knocking trying to find source

shandi235

Hey guys,

I posted back in Oct 2024 had some issues with my oil boiler, I have single pipe steam heat, house built around 1900.

To make a long story short our oil boiler cracked and we replaced it with a natural gas steam boiler + stand alone water heater. This happened in November 2024. We spent the better part of the winter balancing and re-balancing the rads and finally after replacing all the air valves and getting everything just right I can happily report that all my rads are balanced!

However, they knock like crazy. Sometimes violently. I checked and all the supply valves are open 100% of the way, my radiators don't appear to be harboring water at least not that i can tell, but I'd really like to stop the knocking, sometimes the house shakes. What are some tricks that I can try to get this resolved?

I drained the wet return, i got a bunch of clear cold water coming from it and it started to heat up, presumably water inside the boiler was starting to come out. My water level looks okay.

I'm prepared to give you guys as many photos and things as you need just let me know what you want to see. I believe my pressure is set to 0.7? I think that's what it reads.

Intplm.

Pictures of the boiler showing the near boiler piping close and ten feet away at different angles should help.

The banging is most likely sags/low points in pipe allowing for steam and condensate to come in contact with one another. The radiator valves could also be a problem.

The valves could be damaged. Loose or missing discs could obstruct the flow of steam causing this noise.

shandi235

Let me know if you guys need more or some explanations!

Jamie Hall

Nice near boiler piping. At least we don't have to worry about that for a change! Boiler water looks pretty murky, though — another skim or tow and maybe a full drain and flush and refill wouldn't hurt.

But…

I see at least one of the old timey strap hangers. They work fine… for ages. But, eventually, the building sags and they say (old age, you know) and pipes lose their pitch or straightness. I'd go along every inch of steam main and riser and check that the pitch is adequate and that the pipes are actually still straight, and fix anything which is amiss.

Is the vent pictured your one lonely main vent? If so, I'd consider putting a bigger one on there. It won't hurt your careful balancing…

neilc

NBP above the boiler checks out, but that return doesn't look right,

can we take a closer look at the Hartford loop / copper (nipple) train the width of the boiler? if you sit with the boiler while rads are knocking, does the hammer seem to start behind that boiler?

also, it looks like there's no vent on the left main loop,

delcrossv

Good eyes @neilc .

techforlife

Possibly high steam pressure? I can't help but wonder what the Pressuretrol differential wheel is set for under the cover. The sum of that number plus the "cut in" number on the front on the control equal the approximate "cut out" pressure setting. It appears as though the cut in is about 1 to 1.5 psi. You may be running at 2.5 psi or more steam pressure which IMHO would likely be too much. There are those who may not agree with this, but in my 5 decades of experience lowering the pressure has cured the banging in scores of instances. I suggest .5 (Lowest) for the outside cut in setting, and 1 (lowest) for the wheel inside. It is easy to do and costs nothing to try.

shandi235

Hi all here are some more photos of behind the boiler. Let me know if you need more angles I'll get them after work

I set the outside pressure to 0.5, I tried to set it to the lowest setting by twisting the screw but the little metal indicator started to slide out, so I tightened it back until it went all the way back in landing at 0.5

It's still knocking and when I heard it I went down to the basement. I heard and saw only what I can describe as surging, I could hear the water pushing through the boiler as it was knocking and the LWCO light keep flashing on and off, the water in the glass was getting sucked in and out.

tcassano87

the Hartford loop is done incorrectly, should have a close or shoulder nipple and come straight down then tie into the return, not across and behind the boiler.

There could be other reasons for your issues as well but I would definitely re do the loop correctly

shandi235

Thanks @tcassano87 can you be specific on what is wrong in the photos? I'm a novice when it comes to this.

I called the people who installed the boiler, and they are coming out to address it tomorrow, but I would to be more specific than "just the homeowner"

tcassano87

https://forum.heatinghelp.com/discussion/comment/1847609#Comment_1847609

just noticed the water on your site glass is also extremely dirty for a new install. Should definitely be flushed out and chemically treated with SurgeX or a similiar product

Could definitely be the cause of your issues with the extreme surging

shandi235

Okay, so instead of where it is now, I see how it cuts across the back, they should cut the line there as you shaded and have it feed that way? I'll show this to them.

I do hear lots of knocking behind the radiator

shandi235

the install was done in Nov 2024, from an oil boiler, we've been flushing it, but I'll flush it more just gotta let it cool off :)

Intplm.

Flush it. Give it a good thorough skim.

shandi235

Whats skim sorry I'm learning just not quick enough

delcrossv

Things to talk to the installer about:

need a new vent here

need a vent installed here, probably Gorton 1's in both places'

as @tcassano87 says, this copper connection should drop straight down to the wet return

your water quality is bad. Boiler needs to be flushed and skimmed some more.

id also flip this reducing tee so the drain cock aims into the boiler- makes flushing the mud leg easier.

lastly, they should check pitch on your lines to make sure there're no sags or pockets.

shandi235

could the water be from 30 years of oil boiling? I remember when they first installed it ran clear then they added some kind of green liquid to it.

Is the water level too low? im watching youtube videos now and the glass always seems to be filled to about 1" to 1 1/2" from the top!

shandi235

@delcrossv reducing tee so the drain cock aims into the boiler, this thing?

Flip that so it points down?

delcrossv

https://forum.heatinghelp.com/discussion/comment/1847637#Comment_1847637

Yep. Flip the tee so the valve handle points out. Then if you unscrew the valve, you have a straight shot into the boiler.

shandi235

ooooooooooooooooooooooooh I get you, yea ill ask the installer to do that

shandi235

https://forum.heatinghelp.com/discussion/comment/1847617#Comment_1847617

how much water should i leave in the sight glass? where it is now? I want to flush it today and get that gross out

delcrossv

You can drain it all the way and then refill to the middle of the glass. Afterwards run it for a good while to drive out the dissolved oxygen.

shandi235

copy that thanks so much guys for all your support and help. I will report back tomorrow after the installer comes to assess. I assume theyre not going to be able to change the pipe for the Hartford Loop the same day, but hopefully they have some vents in the truck!

delcrossv

Don't let them pour in more Squick (green stuff). Just water.

shandi235

Copy that

neilc

I would also move the makeup water feed line from the equalizer, to the wet return while they're piping back there,

you said, "I do hear lots of knocking behind the radiator", Do you mean the boiler? that's that long high horizontal, have it redone as everyone has drawn, straight up from the floor, and as short as possible into the equalizer,

https://forum.heatinghelp.com/discussion/comment/1847612#Comment_1847612

lastly, buy "We Got Steam" sold here in the bookstore

neilc

oh, and that skim port, have them move the ball valve to the horizontal, leave off the turned down 90, and then cap the valve with a nipple and cap,

you'll have a better visual of skim flow,

shandi235

Hey guys! Update after the boiler guy came.

Hartford Loop is within spec, he showed me in the book and the height, he agreed it did look off and they probably shouldn't have cut across the boiler but it is working. He saw the surging and heard the knocking, water in my sight glass is far too low he suggested to keep it 1/2 filled and see if the surging stops, he filled it to 1/2 glass and ran the boiler for about an hour, no knocking or surging. it's been about 24 hours and the only knocking we've heard is the small "knock knock" that the rads do, nothing like the surging or violent banging we've been hearing.

The other issues, he agreed 100% there needs to be another vent on the main going from the second pipe. Problem, the cap is basically fused into the pipe, they'll have to cut it off and refit it. Going to do that in the summer. The current main vent is old and should be replaced. Again that'll go in the summer.

Pitch on all but 1 radiator is correct, but the bigger issue with the rads is the air vents are on the top instead of the middle of the last piece, making them close way too early. They're going to correct that. One of my rads is leaking, the ball/socket is misaligned, they'll fix that.

The last thing he did was a very long skim and refill, he did put more stuff in it because the water was having a hard time turning clear, he told me let it sit in there for a week or two then flush it out again.

All and all they can do all these fixes in the same day, just need to schedule it, going to aim for May/June to do it, he said all in all the only cost would be the fitting for the capped pipe shoulder about $ in total for the part/labor, everything else hits my new boiler's warranty and no cost to me.

Thanks for all the insights guys absolutely appreciate all the help here. It's always great to be able to bring something to the table and have the repair guy listen to you.