Baseboard hot water boiler making knocking noise

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Old 12-02-08, 09:18 PM
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Baseboard hot water boiler making knocking noise

Greetings all. Recently my Crown boiler started making knocking noises once it fired and began to heat up. It's loud enough to wake me up occasionally, and is very loud in the basement by the boiler. The needle on the pressure gauge actually moves with every knock.

I recently had a heating company out and they drained the water, refilled it and the noise stuck. They were going to replace the acustat (? the thermostat that controls the boiler water temp) but they wanted over 650 to do that so I declined.

I had the pressure release valve replaced on the boiler and the water tank 2 years ago along with a new expansion tank. I will get some pics up of the system if needed.

Any ideas what is causing this? the pressure stays around 15 psi when "cold" and stays at 20 when the boiler is lit. Water temp is around 170. The boiler is not that old, I have only lived in the house 3 years and was told it was replaced about 10 years ago.

there is something installed upstairs on the water pipe right before it runs back down to the boiler. IF you look in the picture below you will see what it is. Its the small canister looking thing right above the expansion tank connected to that green manifold looking thing.



sorry if my explanation stinks, i'm new to this stuff. again i'll get pics tomorrow.


Info:
Natural gas powered
2 story home
2 zones
heat actually is fine, but the noise is annoying and I'm wondering if possibly damaging to the system
 
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Old 12-02-08, 09:35 PM
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The first thing that comes to mind is air in the system. Does it matter which zone is calling for heat? if you are near the boiler, touch various spots when it making the noise to see if you can pinpoint the exact spot. Use gloves in case the pipes are hot.
 
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Old 12-03-08, 12:26 AM
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I see in the background that you have a Well Extrol tank which would lead me to believe that you have well water. This is just a hunch but since you have well water I am guessing that you may have some type of Mineral build up inside the boiler which would result in some "Strange" noises when your boiler heats up.
 
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Old 12-03-08, 06:53 AM
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sorry guys I stole that pic off google so that I could show you what that part was I was talking about that is installed up stairs. I am uploading pics of my setup now along with a little video of the boiler and the noise it is making.

It does not matter which zone calls for heat. It even makes the noise when the hot water tank turns the boiler on.
 
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Old 12-03-08, 07:11 AM
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pics





 
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Old 12-03-08, 07:16 AM
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video...might want to turn up the volume a little.

Video

Right click save as...it won't stream. it's small, 1.4 MB
 
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Old 12-03-08, 07:19 AM
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I see some corrosion on the piece above the tank. Is that a check valve and could air be getting in there.?
 
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Old 12-03-08, 07:26 AM
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Originally Posted by Pulpo View Post
I see some corrosion on the piece above the tank. Is that a check valve and could air be getting in there.?
Are you talking about that little silver canister that is installed basically right above the expansion tank? There used to be a little screw on cap on there but I noticed that it is on the floor. Should that be screwed on tight?
 
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Old 12-15-08, 01:35 PM
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I went through and bled the system but the popping noise is still very noticeable. Any other ideas?
 
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Old 12-15-08, 03:48 PM
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What is the system's pressure, hot and cold?
Doug
 
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Old 12-16-08, 02:46 PM
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hot it is right around 19 and cold it usually drops to like 15.
 
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