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Old 12-22-2010, 09:12 AM   #1
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hydronic boiler bang?


Hi all, my hydronic boiler (pushed by oil) is making a loud bang when it shuts off. Anyone know what this could be? It doesn't seem like there is any air in the lines, and it's keeping the house a constant temp. The loud bang is just sort of scaring me. Anyone have any ideas on how I can get rid of the bang?

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Old 12-22-2010, 09:45 AM   #2
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hydronic boiler bang?


ok, I sat by my boiler to try to listen for the location of the "bang." the bang happened about 2 seconds after the boiler shut off. It's bad enough to actually shake my lines and expansion tank. Anyone have any suggestions as to a cause or fix? Please help

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Old 12-22-2010, 10:01 AM   #3
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hydronic boiler bang?


I assume you mean your boiler is fueled by oil, I don't quite understand "pushed". I have a fuel oil fired boiler, and one time it too made a "bang" sound after it shut off. Turned out that the transformer was cutting out before the fuel pump was, so fuel was being fed into the boiler without a spark. The fuel (kerosene) ignited after a couple of seconds, made a loud boom sound.

I got it fixed by having my boiler repair technician come out. He had to replace some controls, I can't remember if the transformer had to be replaced. Based on what I saw, this operation required a trained technician to diagnose and correct. Well worth the money to have it repaired correctly. I recommend you do the same.
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Old 12-22-2010, 10:35 AM   #4
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hydronic boiler bang?


Sounds like your check valve on the pump outlet is slamming shut.
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Old 12-22-2010, 11:08 AM   #5
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hydronic boiler bang?


thanks for the reply! Is there a way I can check the check valve?
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Old 12-22-2010, 11:27 AM   #6
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hydronic boiler bang?


Sounds like a zone valve closing while the pump is running. Common with Honeywell zone valves.
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Old 12-22-2010, 11:33 AM   #7
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hydronic boiler bang?


Do the pump and boiler shut-down together?, and if they don't does the bang occur when the pump shuts-down or when the burner on the boiler shuts down.
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Old 12-22-2010, 12:35 PM   #8
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hydronic boiler bang?


thanks again for the replies. I believe the bang occurs when the pump shuts down. the pump and boiler shut down at different times
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Old 12-22-2010, 12:57 PM   #9
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hydronic boiler bang?


well I've called a Heating company and they didn't have a clue. I did just install a new programmable thermostat. Any chance the wiring can kick on the boiler and pump, heat the house ok, but be causing the bang noise? It's a honewell stat.
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Old 12-22-2010, 02:13 PM   #10
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hydronic boiler bang?


one more update, I put the old thermostat back on and I had the same result....loud bang as soon as the circulation pump turns off. Please help
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Old 12-22-2010, 02:47 PM   #11
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hydronic boiler bang?


That would indicate the check valve is slamming shut.

Is this the first heating season for you in this home?

Is this a new issue or an existing problem?

Are there multiple zones on this system?

Sounds like you are getting a reverse flow immediately on pump shut-down.

Any changes to the system? other than a new Tstat

Where is the back pressure regulator in the system?

Is your auto fill valve functioning? Pressure at the expension tank?

Sometimes a pic or 2 of the system is helpful for diagnostics.
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Old 12-22-2010, 05:14 PM   #12
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hydronic boiler bang?


jackofall1--thanks for your help. This is the 2nd winter for me in this home. Last year I replaced the circuit board/control box. About a week ago, my circulation pump went bad (bearing i think). I replaced the circulation pump and everything seemed fine for a couple days--no air or gurgling sounds. Then this started happening. There is only one zone on the system. Honestly, I don't know what the auto-fill valve is, or how to check the back pressure regulator or the pressure in the expansion tank. I'll try to post a couple pictures. Thanks again. I've now talked to three people who install boilers and none of them have had an answer for me.
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Old 12-22-2010, 05:18 PM   #13
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hydronic boiler bang?


Jackofall1--here are some pictures
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hydronic boiler bang?-dscf5110.jpg   hydronic boiler bang?-dscf5109.jpg   hydronic boiler bang?-dscf5108.jpg  
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Old 12-22-2010, 05:22 PM   #14
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hydronic boiler bang?


The style of check valve would be good to know, it that valve is spring actuated it could explain why it is now slamming shut.

I imagine you replaced the pump with an identical unit.

Typical example of both back pressure regulator and a fill valve.

http://www.nicinst.co.za/category/pr...ure-regulators

http://www.elocalplumbers.com/blog/b...ill-valve-2899
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Old 12-22-2010, 05:23 PM   #15
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hydronic boiler bang?


one thing that did confuse me was that when I installed the circulaton pump, the old pump label was upside down on the pump. the flow arrows indicated that the pump pumped down (arrows pointed toward the floor). I installed the new pump with the arrows pointed toward the floor as well. Is there any possible chance that I have the pump pumping in the wrong direction?

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