Steam Radiator Knocking Sound

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  #1  
Old 01-24-18, 06:03 PM
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Steam Radiator Knocking Sound

Good Afternoon all,

PROBLEM
  1. There is a heavy knocking sound coming from the radiators and throughout the boiler loop, it's keeping myself and family up at night.
  2. Bedroom 1 & 2 radiators won't heat up.

SYSTEM DESCRIPTION
I have a Burnham Gas boiler in the Basement and 5 radiators on the Top Floor. The radiators were distributed in the Living room, kitchen, bathroom, bedroom 1 and bedroom 2. I also have baseboard heating attached to the boiler, pushing hot water throughout the basement via a Bell and Gossett 100. pump.

STEPS TAKEN
  1. Turned off the boiler and opened all 3 drain valves surrounding the boiler to drain the boiler circuit.
  2. Manually refilled the boiler and until the glass level reads mid-level, turned boiler switch on and observed auto fill activated and stabilize at the mid-level mark.
  3. Adjusted the thermostat in-house temperature to 4 degrees above atmosphere temperature to induce boiler. Within 30 mins the knocking sound came back loud throughout the entire house.
SUMMARY
We've had this boiler for 3 years now and this is the first time that we've had this problem. Would really appreciate your thoughts?

Thank you,
Addanis
 
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  #2  
Old 01-24-18, 06:20 PM
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More pics of the boiler and piping would be good.

With the limited info it sounds like the steam going to the rads is meeting the condensate coming back to create small explosions for lack of a better word inside the pipes.

This could be caused by pipes being pitched the wrong way or incorrect near boiler piping, dirty boiler boiler water surging and possibly syphoning up into the system.

All pipes should be pitched back towards the boiler to drain the condensate.

Is this something new or an ongoing problem.

What is you pressuretrol (silver box with glass front) set at.

Radiator vents must get rid of air before steam can enter. If no heat in 2 rads, check vents.

You should hear some hissing which is the air releasing and then the vent should shut and heat up. It should not continuously hiss either or it is defective.

What you can do to see if it is the vent. Shut the boiler down to cool. Remove the vent from the rad. Turn on boiler and see if rad heats right up being careful not to get burned when the boiler is on.

If the rads heat up you know it's the vents that must be replaced. Shut the boiler down and when safe reinstall the vents until replaced.

Hope this helps a little.
 
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Old 01-25-18, 02:24 AM
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As @Spott stated, pictures and more information is needed. Is this a 1or 2 pipe steam system, It makes a big difference in the answers we will provide. (how many pipes go into a radiator). Is this banging a new problem? If so when did it start happening? .What is the normal operating steam pressure and has it been changed?
 
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Old 01-25-18, 07:11 PM
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Radiator knocking

Thank you all for your responses to my inquiry, please excuse the delayed response. I uploaded more pics in the form of a collage.
This is the first time since we installed the boiler 3 years ago that we are experiencing this knocking sound throughout the boiler system.
I did notice that the boiler sight glass level is intermittently over filling, pass the top level. Since the heating season started, I would occasionally have to drain the excess water when I notice it.
In addition, I would hear water "Swooshing, swashing" around in our bedroom radiator, followed by the knocking. I tried to drain the boiler circuit before and refilled the boiler with fresh water. It seemed to work fine, until the knocking sound came back and would eventually fill the sight glass pass the top level.
Your thoughts and suggestions are appreciated.
Thanks/ Addanis
 
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Old 01-25-18, 08:03 PM
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a,
I am seeing a couple things here.

First, you have an auto water feeder that may be malfunctioning and overfilling your boiler or the LWCO is calling for it to come on for some reason.

What I would do is shut the valve off at the auto feeder and feed by hand to see if that helps. That swooshing you hear is water in your pipes that shouldn't be there and when the steam hits it that creates the knocking.

Drain your boiler to about half the glass and leave the auto feed valved off so if it calls it can not let water in and see if that works. That should stop the knocking.

Next, on your pressuretrol. Can you see if it says the differential is additive or subtractive.

I believe your is subtractive. If so your pressures are a little high.

I would adjust the main dial to 2 psi(it is @ 3 now), and set your differential to 1.5 psi.

What that will do is shut your boiler off @ 2 psi which is all you need and will turn it back on @ .5 psi so it won't short cycle as it's probably doing now.

With your settings now it's shutting off @ 3 and coming back on @ 1.75 psi. Too high, waste of fuel.

On a side note you might want to cover your pipes coming off the boiler to keep the steam in the pipes as long as possible to get to the rads. Without the covering the minute the steam leaves the boiler and enters the pipes it starts to cool down to make condensate instead of getting up to the rads. Waste of fuel, making steam that never gets to the rads.

Just my thoughts. Hope this helps a little.
 
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Old 01-27-18, 06:16 AM
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Steam Radiator Knocking Sound

Thanks Spott for your advice,
  • I drained the boiler glass level to a half and closed the valve to the auto feeder. The banging minimized a bit, thank you!
  • I will attempt to calibrate the Pressuretrol and order covers for the pipes as per your suggestion.
  • Will monitor the system in hopes that the banging will totally disappear and give an update.
QUESTION:
  1. Can I repair the auto feeder or do I have to replace it?
  2. Is there a calibration involved with replacing the auto-feeder?
 
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Last edited by addanis; 01-27-18 at 06:46 AM.
  #7  
Old 01-27-18, 08:32 AM
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a,
Is your LWCO still calling for the feeder to come on? There may be nothing wrong with the feeder.

With your water possibly syphoning up into the pipes or surging enough for the LWCO to call for water it may have been doing it's job.

Check to see if the light comes on, on the feeder which will tell you if the LWCO is calling. If the water stays stable it probably won't call.

If it does call there are adjustments, delays, that can be made to the feeder so the water has a chance to come back before it feeds more water in.

The easiest way for you to learn about this is to go to the sight below and you can read all about it.

On the sight scroll down to the manuals and it will explain everything about it including the dip switches to make adjustments. Don't give up on it yet.

http://www.supplyhouse.com/Mcdonnell...ter-Feeder-24V

Hope this helps a little.
 
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Old 01-29-18, 08:28 PM
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Thank you Spott, for your previous response! Please see below for the steps that I took since then:
  • I confirmed that my LWCO accurately calls for water and will cut off the automatic water feeder at the mid point on the sight glass.
  • However there is a slow leak from the automatic water feeder without activating the LWCO. The additional water floods the boiler and steam circuit.
  • I tried to remove the strainer/ orifice to see if it needs cleaning, but was difficult to remove. I plan to order a new automatic water feeder and replace the malfunctioning water feeder.
  • While troubleshooting the line, I noticed that the automatic water feeder was connected to the Cold Water line, while my by-pass valve was hooked up to the hot water line. To promote energy efficiency, wouldn't it be better for both lines to be hooked up to the hot water line?
  • Also, I downloaded the pdf to calibrate the L404F Pressuretrol, but was a bit confused about performing the calibration; not sure if I had to open the Pressuretrol module, or adjust the screws at the top of the Pressuretrol?
Any advice you can give is appreciated.

Thanks/ Addanis
 
  #9  
Old 01-30-18, 10:06 AM
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a,
You adjust your pressuretrol from the screws on the top of the control. There's is no need to open the cover.

It looks like your differential is subtractive so set your main (right side) to 2, and your differential (left) to 1.5.

That will give your a high limit and shut your boiler off at 2 psi which is all you want if the stat is not satisfied yet and the boiler will come back on at .5 psi.

As far as feeding with hot water it's something I never thought of. Boilers are always filled with cold water and I don't know why they would have a hot water line going to your feed line at all. My guess is the line was just convenient to tie into the feed but is valved off and not used except for the bypass.

Where is that hot water line coming from. Something must be heating it up to begin with, using energy.

Your boiler heats up the water so fast there is really, I don't think, much sense in using energy to preheat the water when the boiler heats it up that fast anyway.

Just my thoughts.
 
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Old 01-30-18, 10:36 AM
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@addanis
If what was already suggested here does not help with the banging, I would pour a special boiler cleaning chemical into the boiler, let it circulate for a week and drain.
 
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Old 01-30-18, 10:45 AM
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I'm not a big fan of chemical cleaners, especially in an old system like yours. It could loosen up a bunch of crap (technical term) and create leaks in the old fittings.
 
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Old 01-31-18, 06:26 PM
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Steam Radiator Knocking Sound

Thank you all for your responses! I've learnt alot about steam boilers and how they function through this chat, google and youtube. Still have alot to learn and appreciate your expertise. With that being said I would like to provide an update with my recent findings:
  1. I've been manually filling the boiler as I am not sure if my automatic feeder is defective. Excess water is definitely getting into the boiler and I am trying to isolate the problem.
  2. I frequently check the fill level on the sight glass during the day since deciding to manually feed the boiler. As much as twice a day I noticed that the LWCO red light was steady on red, indicating the need for water. I filled the boiler until the red light disappears and the sight glass water level was in the middle, then turned off the water. At other times the sight glass water level is over the top, indicating that there was too much water in the boiler. Since the valves surrounding the automatic water feeder and manual feed line were closed; I presumed that the excess water was due to residual water in the pipes returning to the boiler via gravity, thereby flooding the sight glass, inevitably over-filling the boiler. I'v observed this residual water over-filling the boiler on Saturday January 27th, 2018, when I initially switched to manual fill and today, Wednesday, January 31st, 2018. Not sure if my I am correct? If this is not the case, then I am not sure how or why my boiler is overfilling as the auto feed circuit was isolated and the manual feed valve was closed.
  3. I also noticed that when the sight glass was filled over the top, only 3 out of my 5 radiators were functioning with heat, the other 2 in the bedrooms were cold. Only when I drain the sight glass to the mid-point line and initiate the boiler that all the radiators started to produce heat.
  4. There is still a knocking sound throughout the radiators and boiler circuit, I now understand that it is because of the excess water in the line.
  5. I also observed that after filling the sight glass water level to the mid-point line, that the water line was visibly bouncing up and down, not staying steady. Not sure if this is normal as the water is being drawn into the boiler to create steam and this is all part of the reaction?
  6. I was about to purchase a new water feeder as I suspect that the feeder valve was not closing properly and water was slowly seeping into the boiler. Will hold off on this purchase until I am certain!
Your thoughts are appreciated?

Thank you,
Addanis
 
  #13  
Old 01-31-18, 07:01 PM
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Have you lowered your pressuretrol yet. Your bouncing or surging water in the sight glass is not normal but a sign of dirty water and should be skimmed, not just drained but skimmed.

If you go on you tube and search steam boiler skimming you can watch the videos. Easier than trying to explain it.

It sounds like your water may be getting syphoned up into your pipes which is why you're getting the knocking and no heat.

Is it possible to get some good pics of the pipes coming off the boiler and where it goes, at least for a short distance.

The near boiler piping is very important and there are dimensions that must be followed so you get dry steam to your rads and not water.

If you are adding water twice a day and you have no leaks you have a problem either with design or dirty water surging into the system.

A normal steam boiler actually needs little water replacement.
 
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Old 02-07-18, 08:42 AM
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TO @SPOTT, I have been watching your conversation and starting to wonder if the installer screwed up the near boiler piping when they installed the new boiler? I haven't seen where "addanis" has said if this is a 1 or 2 pipe system. Pictures of the whole boiler may shed some light on the type of system and the connected piping. Also I would like to know the age of the house, the old boiler the Make ,model, input, and such. Before I make a comment more information is needed. If the old boiler was physically larger (more water capacity) that could be a huge problem, depending on the overall system. Most contractors have no idea how to size a steam boiler, since it is not the same as a hot water boiler.
 

Last edited by Steamboy; 02-07-18 at 11:25 AM. Reason: one more thought
  #15  
Old 02-07-18, 09:34 AM
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S,
There are unanswered questions and expanded pics of the boiler and near boiler piping were requested and I think would be very helpful but as of yet haven't seen or heard anything new yet.

He must be busy or got results elsewhere.
 
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Old 02-17-18, 06:48 PM
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addanis, im having almost the same exact problem as yours. 2 upstairs rooms arent heating up.
 
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Old 02-17-18, 07:03 PM
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@tumbz..... you have your own thread. Best to keep questions pertaining to your problem there.
 
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