Water Hammer after Work on Boiler System

TeresaC

I recently had some work done on my heating system, having three new radiators installed and then some follow-up problems. After the first follow-up (or perhaps it was after the radiator installation - I forget), I started to hear loud banging (water hammer) in at least two of the old radiators; prior to this work, I never had any problems with water hammer in my heating system.

I have read online about possible causes and solutions to this problem, but I would like to see whether anyone out there can help me narrow things down before I attempt a costly guess-and-check approach. Below are all the details of what has occurred. I know it is a lot, but I wanted to be thorough.

I have a steam boiler with one-pipe radiators. The boiler is rated to 5 psi and is about 15 years old. It was last serviced October 2020. There are 3 old radiators in the system and 3 new ones. Prior to the recent installation, I was heating my house with only the 3 old radiators.

In December 2020, the 3 new radiators were installed. The piping had already been in place, so only the radiators and their relief valves were new; nothing else was added to the system. However, the plumbers had to cut one of the pipes to the second floor because it was too long to connect to the new radiator. After the installation, the only “problem” I recall was that the rooms with new radiators smelled like oil when the heater ran, but the plumbers told us this was normal and would fade over time. Also, I think the sight glass (gauge glass) on the boiler looked a little dirty now.

About one week later, the relief valves on two of the old radiators broke and spurted out dirty water. (The two valves did not break at the same time; the second one broke about 18 hours after the first.) After the first relief valve broke, I immediately turned off the heater and called the plumbers; a few minutes later, I turned off that radiator. When the second valve broke, I likewise turned off the radiator (perhaps while the heater was still running - I do not remember - it was the middle of the night). When the plumbers came a couple days later (12/18/20), they discovered that the pressure switch on the boiler was broken. So, they replaced that and the two broken relief valves. They tested the heater, which seemed to work fine.

The next morning, I woke up with my house at 55 degrees. I called the plumbers, and after some questions they said that the blow down valve may be getting old. They suggested smacking it with a hammer; the boiler kicked on a few seconds after I did so, which supported their idea. However, the heat shut off after a couple minutes. Numerous smacks to the blow down valve later (with the heater running for less and less time between each smack, until it was on for only seconds at a time), I started to question their diagnosis. I asked whether the pressure switch could be set too low. The plumbers said I could raise it up to no more than 5 psi. (It was set around 2.5 psi.) I turned it up, and the heater immediately started running. I set it just below 5 psi, and everything seemed to work well again. The plumbers said they wanted to visit in a few days to make sure everything was OK.

As I recall, this is when the loud banging began (before the plumbers came back to make sure everything was working well). I could hear it in at least 2 radiators - the same 2 old radiators whose relief valves had broken. Every cycle, it starts about 30 minutes after the heater first turns on, somewhat early on in the distribution of steam to the radiators. Preceding it, something in the basement (the pipes?) creaks. Then, a little later, the banging begins; sometimes it sounds more like grinding than banging. It is worst when I first hear it, and then it slowly dies down with each subsequent distribution. After so many distributions (a bit before the heater turns off), I don’t hear it any more.

As the plumbers said, they came a few days later (12/22/20) to check the blow down valve. After several tests (for good measure), he said it was working fine. (I do not remember whether I mentioned the water hammer at this point. The bill from that visit does not mention any work done to fix that problem.)

Not sure what to do about the banging, I tried to live with it for a couple weeks, at least through Christmas and New Year’s Day. However, I noticed that it was getting worse as time went on. At one point, it was waking up my family in the middle of the night. In addition to the usual time during the cycle (about 30 minutes in), once or twice I had heard a rather loud bang in the basement shortly after one of the distributions ended. So, I called the plumbers again.

They came on 1/11/21 and blew down and skimmed the boiler. They also raised one of the trouble radiators to give it better pitch; they said the second radiator had good pitch and did not need to be adjusted. I also mentioned that some of the relief valves (the two old, banging radiators with new relief valves and one new radiator) had been dripping more than what seemed to be reasonable. The plumbers agreed and replaced the valves.

After this visit, the banging continued, but it did seem to be quieter. It was no longer waking us up in the night. However, about one week later, I could tell it was getting worse again. I tried lowering the pressure on the pressure switch to about 3.5 psi; the banging got better at first but then worse after several days. I turned the pressure down to about 3 psi with similar results. A few days ago, the banging woke me up in the middle of the night again. So, I am considering calling the plumbers again, but I wanted to ask around before doing so.

As a final “clue,” it seems notable that the banging was a lot less last night just before I went to bed (just some soft pings). What was different? The only thing I can think of was that I decided to put more water into the boiler than I normally do after blowing down the system. (FYI, I do the blow down regularly, once or twice a week. Usually, I do not fill the boiler up to the max. level, but this time I decided to get close.) However, tonight the banging is definitely back to its normal level.

Thank you for taking the time to read this long post. I appreciate what help anyone can give me.

JUGHNE

Can you post pictures of your boiler showing all the piping floor to ceiling, include the blow down device and pressure control and gauge?

Jamie Hall

And turn the pressure down. The boiler should cut off on pressure at no more than 2 psi. Someone -- so it might as be me -- will also suggest that the pigtail -- the connection between the pressure switch and the boiler -- should be checked to make sure that is open, so the pressure switch can sense what the boiler is doing.

neilc

#what?
withdrawn

TeresaC

Here are the pictures. I don't want to turn the pressure any lower because before when it was at 2.5 psi it wouldn't run.

SchenleySeven

Also, too much water in my 5 year old boiler will cause water hammer. I watch the water line in my site glass to be 2/3 of the height of the glass.

I don't see any vents on the two mains?

KC_Jones

Does one side hammer worse than the other?  If so is it the red or the blue in the marked up picture I attached?

EBEBRATT-Ed

@TeresaC


When the plumbers installed the radiators they probably got some dirt and cutting oil into the boiler water. Skimming will help that.

Also have them take the "Pigtail" out and clean or replace it. It's the curly piece of pipe under the pressure control could be plugged making the control act wonky.

Also the boiler isn't piped righ but that's for another day

Check "find a contractor" on this site

Post where you are located someone may have a recommendation

bburd

Remove the cover from your pressuretrol and check the setting on the white wheel inside, this is the differential. It should be set to 1.

The usual settings are 1.5 lb cutin and 1 lb differential.

Excess steam pressure results in water stacking up in the return drips and getting into the steam mains, causing the gurgling and banging you are experiencing.

TeresaC

@SchenleySeven

I usually have the sight glass filled between 1/4 and 1/2 way. So I do not think that is the problem. Can you elaborate on your comment about no vents on the mains? I am not sure what you are referring to.

@KC_Jones

The red side is worse, but the blue side gets its fair share. If it matters, one of the problem radiators (the larger one) is on the red side, and the other problem radiator (smaller) is on the blue side. Both problem radiators are the farthest from the boiler on their respective sides (red one on the first floor and blue one on the second floor).

Jamie Hall

Given the boiler piping, I'd be surprised if it didn't hammer -- particularly the red side. I don't think you have much hope of getting rid of the racket until you get that boiler piped right.

JUGHNE

The pigtail should have been cleaned on the service work done in October, maybe- maybe not.
The blow-down LWCO device may need cleaning also.
The gauge shows negative 5...obviously not accurate.

The control needs to adjusted inside the box also as mentioned above.

The skimming probably should be done even several times.

All the pipes should be sloped to drain back to the boiler....starting with the high point above the boiler and then all the way back to where the copper returns connect to the bottom of the boiler.

KC_Jones

I'm going to throw this out there.
Rads added, more condensate.
Completely wrong near boiler piping that is absolutely throwing water into the system.
The new added rads simply overwhelmed the piping's ability to handle the condensate and now it bangs.
The red side being worse agrees with this. The blue side has a "drip" on that main at the boiler to allow some condensate back down.
Solution, in my mind, re-pipe the boiler.

I don't disagree with skimming, that is most likely adding to the problem. If skimming solves the problem that would be incredible and add to the feeling of how forgiving steam can be.

mbachelor

I am also experiencing hammering after having the hot water loop off my steam boiler replaced. I was told a skim and squip could resolve the issue (but no guarantees). I also never had hammering prior to this replacement. Is it possible that there is just air in the line causing the hammer or do people think the skim and squip will actually resolve the hammering? The cost for skimming was a lot higher that I expected so I was curious to know if air was the issue if I could somehow remove it and avoid the costly skimming.

Jamie Hall

@mbachelor -- You may need a skim, but the no guarantees bit is correct. Squik won't help, and, unless the boiler is completely drained and refilled after using it may actually make the problem worse.

However, that said, where is the hammering coming from? The steam lines, or the hot water line? If it is the hot water line, then perhaps there might be air in it, which could be cleared by purging that line.

;The purpose of skimming is to remove any oils which may be on the surface of the boiling water, leading to big bubbles and burps. It is not at all difficult to do, but does take time -- it can take hours -- and if you are paying a tech. to do it, it's going to cost much money. It has nothing to do with air.

pecmsg

@mbachelor

Time to look for a "Steam" professional. Adding emitters but not addressing the near boiler piping is a huge RED flag.

mbachelor

thanks, Jamie. the hammer is only coming from the hot water loop. is purging the line something i could do? i added a few pics below-the pipe above the blue line is the hot water loop that runs up to the first floor.

Jamie Hall

Purging the new hot water line may -- or may not -- be easy enough to do. It depends on where you have valves on the line, and whether it is using boiler water directly or is heated through the boiler's tankless coil ;or a heat exchanger.

Therefore -- before I go further -- could you provide a description of how that hot water loop is piped and pumped?

KC_Jones

@mbachelor may I suggest starting your own thread so we don't hijack this one and keep the answers to the OP clear.

mbachelor

@KC_Jones-yes, absolutely I will start another thread. i apologize-i didn't mean to hijack OP!

EBEBRATT-Ed

@KC_Jones

is 100% correct!

The boiler and piping were quiet until the extra radiation was added. The near boiler piping worked at lower load because it didn't have to handle as much steam or condensate.


This is why we find a lot of old boiler with the wrong piping that work quietly because they are way oversized in comparison to the load.

TeresaC

I had wondered whether the addition of new radiators might be the problem. However, I already tried turning off all the new radiators for one run, and the water hammer was just as noisy.

TeresaC

I took the cover off the pressure switch. How can I tell what value it is set to?

EBEBRATT-Ed

If you look at the white dial the differential is set to 1psi where it is now. That should be ok. The cut in setting should be at .5 pounds.

Problem is the scale on the pressure controls are fairly inaccurate. I would leave the diff where it is and set the cut in to .5 and try it.

If the boiler doesn't start with the thermostat calling raise the cut in a smige

neilc

turn the white wheel counterclockwise as you look down on it the way we see it in the picture,
don't force it,
you are either set around 7/8, or already at 1 ish,
counterclockwise as you look down on it, gently,
use that screw with the mark under it as your indicator.

then check and clean the pigtail,
you should be able to breath into and thru it, back into the boiler,
or pour water back thru, into the boiler,
check, and clean it if needed

kenlmad

You have two large issues thwarting your efforts. All the other small problems are amplified by these issues, unfortunately.

Large Issues - Not DIY tasks in +99% of the human population, but you never know.
1. The near boiler piping is wrong and promotes hammering. (+$$$)
2. Your boiler is likely to be 2x to 3x the necessary size. 650 EDR for 6 radiators seems extreme. Replacing the boiler. (+$$$$)

Smaller issues - you can inspect and fix yourself
1. Skimming - buy one of Dan H's books in the store on this site. Read about it in The Wall, or Google search for some videos so you can be confident that its done correctly. You really should attempt this first before any of the other smaller items. And plan on skimming 3x or more, 1 per week for the next 3 weeks. You need to get all the residual oils out and it can take time for them to get fully rinsed back to the boiler. Luckily, it looks like the boiler already has the skim port plug removed and has a capped pipe in place. (free)


2. Verify that all the radiator steam supply valves are fully open or fully closed if you don't want that room heated. No "in-between". Partially opened can cause hammering, albeit local to that radiator. (free)

3. For the side of the house that's banging, try lowering the Air Vents to a slower setting to reduce the rate of condensate. If you have adjustable Air Vents this is simple. (free or +$)

4.

TeresaC said:

I took the cover off the pressure switch. How can I tell what value it is set to?

That differential looks like it is set correctly to 1 PSI. Set the Cut-In to 0.5 PSI. Use the adjusting screw on top but stop turning the screw when the steel indicator bottoms out in that slot. If you keep turning, a PITA nut shortly falls off on the inside and takes time to put back together. (free)

5. Verify that the pigtail is not clogged. That's the curly brass pipe under the grey Honeywell pressuretrol switch. There's plenty of resources online that show how to DIY. (free)

6. Your pressure gauge does not appear to be working properly. It's reading -5 inches of mercury which seems odd to me, but not impossible after the boiler ceases firing and starts to go negative pressure. But if it doesn't go to 0 PSI when it's not hot, it's broken. Even when new they are inaccurate and misleading when trying to troubleshoot. Replace the gauge with another 0 to 30 PSI. (+$)

7. AND add a lower pressure gauge 0 to 3 PSI is preferred, 0 to 5 PSI is ok. (+$)

8. At this point it may be worth trying to find the boiler water level "sweet spot". But there may be no hope given the condition of the near boiler piping that is begging for water to enter the steam pipes. (free)

9. Main Vents - not sure there are any. May need new fittings to add them. DIY is TBD (+$$)

I hope this helps.

EzzyT

Start with correcting the near boiler piping adequate main venting and insulated the piping then go from there. Skimming the oil out of the boiler is a must and should be done when a new boiler is installed and whenever new piping potentially is replacing old piping.
But again the elephant in the room is the near boiler piping.
Every system starts with a Heart and that is the boiler. 

That’s my two cents.

TeresaC

I decided to skim my boiler two nights ago after searching online for some good instructions. Ever since then, I have not heard any banging! I will take kenlmad's suggestion and skim two more times over the next two weeks just to make sure I get it all out. As I said in my original post, the pattern with "fixes" so far is that the banging gets quieter at first but then is loud again after a week or two; so, I will keep an eye (ear?) on it to be sure, although this is certainly the best result by far.

Thank you all for your suggestions. I will let you know the final result in a couple weeks (hopefully).