knocking sound


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Old 12-02-23, 06:54 AM
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knocking sound

Hi guys,
I have this simple question with my boiler. The left one with 2 zones. When I use the boiler for the basement, sometimes I have this knocking sound on the radiator (Which happens to be the last one of the basement circuit but not sure if it's important to mention it).

This sound always makes me think of the movie WTC of Nicolas Cage when the guy tries to pull a metal rod to provoke a sound. The sound might not be exact same but still it's a knocking sound and it comes once a while.

This boiler water pressure is just fine.

Should I do a system water dump (on basement circuit only?) or any thoughts? Thinking about it, I'd say there is a little air in the basement circuit.

Thank you very much

 

Last edited by intiko81; 12-02-23 at 07:19 AM.
  #2  
Old 12-03-23, 05:42 PM
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The circulating water should not be randomly replaced as it's full of air that will need to be removed.
If you have air in the system.... yes... bleeding it out is required.
 
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Old 12-03-23, 07:31 PM
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Hi sir,

Well the green circulator of the left one boiler never been replaced and it's working just fine for both basement and first floor. I only have this random knocking sound on the last radiator in the basement's zone when the boiler is on... nothing more. I don't think it's an alarming situation but I might be wrong.

Now that I have 2 zones, one for the basement and one for the first floor, I should have the purge on the last radiator of the basement too. I will check it tomorrow.
 
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Old 12-04-23, 01:15 AM
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Also, this sound often comes when I turn off the thermostat (basement). A sound comes out of the radiator (which happens to be the last one of the circuit). Thought maybe someone has experienced that sound.
 
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Old 12-04-23, 07:54 AM
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Does the sound occur immediately when the boiler starts or the thermostat goes off? If there is a delay, it could be caused by pipes expanding or contracting as the water temperature changes.

One of the 2 inch iron pipe risers in my 1912 hot water system sits on a beam in the basement. When the pipe heats up and expands above there is a loud bang that sounds like it is coming from the cast iron radiator. When I hear it I know the heat is on.
 
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Old 12-06-23, 06:33 AM
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Hi, sorry for the delay. I didn't have the time to test but last night I was there.

Now I'm confused because during last night I could hear like 4-5 consecutive bang in a span of less than a second... bang bang bang bang. It happened a couple of time during this night. Sometimes a single bang can be heard too when the boiler starts. It's tough having to waking up at night each time it happens to check if it's when the boiler goes off or on that happens. I saw the circulator running yet I heard a single bang.

Although the room temperature showed on the thermostat (old one with mercury - soon to be replaced with a Sensi smart) , I have a feeling that I wish the room was a bit warmer, maybe it's just a feeling. I still get a hot water returns to the boiler tho

I might check the radiator later or... bleed water again? The last time I did it was like 2 years ago when I replaced the boiler (Thx for Pete from this forum for helping me connect back all sequencers of the new boiler)

Edit: I just read a website, they speak of air in pipes when we hear some bang... I'll check that

 

Last edited by intiko81; 12-06-23 at 08:12 AM.
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Old 12-06-23, 07:24 AM
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This rise a question, if I had to bleed all water just to make sure I'll have a cleaner water inside my circuit, do I have to do for the entire zones or can I do it just for a specific one? I have 2 zones, one for the basement and the other on the first floor.

What would be the best approach? I know each zone valve can be manually closed if I had to stop the breaker for maintenance.

Last... I have replaced the expansion tank of the other boiler and it's just slightly inclined. Do I have to absolutely correct it? I'll post a pic later. I know the expansion tank should be vertically positioned.
 

Last edited by intiko81; 12-06-23 at 10:15 AM.
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Old 12-06-23, 11:21 AM
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If necessary, each zone can (and should) be flushed individually. However air can be bled out at radiators (preferred) with proper bleed valve without flushing the entire zone. Pump shouldn't be running when bleeding.

Do you have Honeywell zone valves. They can cause water hammer (banging) when closing. That can be reduced by removing one of the springs. I have one that does that. After removing a spring the sound is more a "thump" than a "bang."
 
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Old 12-06-23, 02:05 PM
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Thank you for the reply.

Tomorrow I will look for that bleed valve. I know there is one for the first floor (highest point - kitchen) but I will look in the basement if there is one for that zone specifically. Garage has a radiator that is at around 4 feet height.

Otherwise I will go for dumping water for that zone at the end.

I have the Motortrol 672b for the basement - apparently hard to find any reference to it. The first floor has the 1361 of White Rodgers.
 
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Old 12-06-23, 02:38 PM
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A high point in the basement may be above a radiator. In that case the bleed valve or an air separator may be at a high point in the piping before it drops to a radiator.

You will also have to increase the pressure in the system through the water supply valve as you bleed to make up for lost pressure.
 
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Old 12-06-23, 04:20 PM
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Indeed I will monitor the pressure if I have to bleed. I do have the reducer valve to supply water when needed. It usually kicks on by itself when the pressure is too low.

Also, I changed recently the expansion tank of the other boiler (right one) and as we can see it's not 100% vertical as the piping isn't originally. Should I correct this or not? (Cause expansion tanks should be fixed vertically only - upside down or normally). This boiler has a pressure around 19 when off and around 22-23 when running. It's for the second floor. If I had to lower the pressure a bit, I can simply flush some water from the service valve down there I bet? I have been doing it like slowly.. the pressure goes down a bit while flushing but when I close the valve, it goes up again to around 19. I don't want to end up flushing all water too as I don't know how much is left in the pipe. I'm just asking questions here and here just to make sure it's okay what I'm doing.

Right one on this pic.

 

Last edited by intiko81; 12-06-23 at 04:54 PM.
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Old 12-07-23, 09:21 AM
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Sometimes the automatic pressure from the reducer valve does not react quickly enough when bleeding air. Boosting the pressure an additional 3-5 pounds by using the lever on top of the valve can help. When air is all out you can then just let water out if necessary until the pressure goes back down. Even after you do that the pressure will read higher when the boiler is hot and back to normal when it cools off.

19 to 23 is an OK range for a second floor system.

The position of bladder type expansion tanks like yours is not critical. They do not depend on gravity. If it is a little bit crooked it is not a problem.
 
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Old 12-11-23, 07:18 AM
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Hi,
Here a quick update. I did the water flush for that second zone (basement) and everything went smooth. The reducer valve kicked on when the flow was high.. it allowed me to renew the water and it was really dirty. After letting the water circulating for a good moment, I just closed the service valve and the pressure went back to normal (around 10-11PSI when off). I think both reducer valves are set differently. The basement/first floor boiler has its reducer set to factory - 12PSI.. Then the other boiler for the second floor has it at around 18.. Then once each of them are on, it goes up a bit of course.

Now yesterday I had the chance to be there for the whole night, and I think I found the problem. The bang could come from the zone valve like you mentioned. I can hear and feel it with my hand. Probably got stuck sometimes for a moment when trying to open or close. Sometimes it's a one bang and sometimes it's a four consecutive bangs. I couldn't be there when it's a 4 consecutive bangs (too sleepy lol). I will try to manually open it and close it next time and see if it helps.

The zone valve is a Motortrol 672b. It's hard to find any ref but results in Google shows many of them look like mine and I'm pretty sure mechanically they are all the same. At best I will try to open it and check the mechanic inside.

Last... If I have to change that zone valve, what would be a recommended one? Or they are pretty much all the same? That zone valve is a simple one compared to the other one (1361 of White-Rodgers)

 

Last edited by intiko81; 12-11-23 at 09:00 AM.
 

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