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Old 03-02-2012, 10:35 AM   #1
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Banging return line


Just had the plumber install 2 new air vents on the return lines (2 zone) to the boiler because of corrosion. Now the return line for the downstairs zone (with new automatic vent) bangs and shakes towards the end of the heating cycle. Sounds like air in the line but since its an automatic vent I don't think there is a way to manually verify this.

I'm have a Peerless Boiler with a Fill-Trol expansion tank. The air vent on this
unit was not replaced and there is "crud" under the plastic cap. I think I should replace it, but not sure this would solve my problem. The pressure on this tank unit is currently 20-22# .

Not sure what to do next Suggestions?

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Old 03-02-2012, 11:15 AM   #2
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Banging return line


Air in the system will usually give you the sound of running water in the pipes. If its so much that it creates an air lock then one or both of those two zones will stop circulating and then the boiler can make some noice.

What is the temp & pressure on your guage when the boiler is operating each zone seperately? That info will help us diagnose the problem.

A lateral heating pipe that is sticking on anything (a hanger) can make a banging sound as the heat expanding pipe breaks free of what ever it was binding on.

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Old 03-02-2012, 12:34 PM   #3
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Banging return line


I just cycled it on and temp dipped to 160 and rose as high as 195 by the end. The pressure runs between 15 and 20 psi.

When the temp and pressure get up toward the end of the cycle, the noise starts. The sound is more of a metallic clanking and seems to come from the area of the Air Purger mounted to the expansion tank. When this happens the pressure gauge starts to twitch.

The return line just seems to be the one that shakes the most when this occurs.
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Old 03-02-2012, 01:04 PM   #4
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Banging return line


The press looks fine. Does the pressure get up above 25 - 27 at any time?

The temp is spiking. If your guage is accurate then I would be looking for a restriction in the water flow. Check that all the gate valves that were turned off for the previous repair were fully opened up again. The only ones that might justifyably be partially open would be for a crossover from the supply to the return or a mixing valve.

Many auto bleed valves have what looks like a bicycle tire valve on the top of them. With your fingers unscrew the little covering cap to that air bleed valve and try pressing in the nib on the stem the same way you'd let some air out of a tire.. It will just spurt water if there's no air in that line or air if its there. Do this while the pump is off.

Also tell us what the aquastat contols are set at for operating temp and upper limits.

Last edited by how; 03-02-2012 at 01:37 PM.
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Old 03-02-2012, 01:42 PM   #5
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Banging return line


Thanks. I checked each of the automatic air valves and there is no way to manually trigger them.
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Old 03-02-2012, 02:56 PM   #6
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Banging return line


pressure never gets near 25-27. All valves open. Don't know how to check Aquastat settings, these are for the hot water system - correct?
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Old 03-02-2012, 03:24 PM   #7
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Banging return line


A picture with the boiler door off would help.
Aquastats control the temps in the boiler by turning off the power to the gas valve when the temp goes above a preset range. They will either be in the boiler (usually above the gas valve) or on top of the boiler. They will usually have a dial or a temp scale that can be adjusted. Typical settings would be 140F for an operating temp and 160F for an upper limit.
Sometimes both controls will be combined into one control that performs both functions. Your temp going up to 195F was why I asked you where the were set.
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Old 03-02-2012, 03:37 PM   #8
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Banging return line


Got it. Settings are:

180 HI 160 LOW AND JUST A HAIR ABOVE 15#
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Old 03-02-2012, 04:03 PM   #9
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Banging return line


Try turning down the 160 to 150 & the 180 to170F to see if it lessens the banging & shaking of that return pipe. And while you're around the boiler try tapping on the both ends of the expansion tank to see if one half sounds full and the other half sounds solid.
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Old 03-02-2012, 04:07 PM   #10
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Banging return line


Will try charging the settings. Already tried banging on the expansion tank,
but it's hard to tell....
Bottom sounds hollow, top solid. I checked it's pressure - 22# if my tire gauge
is accurate.
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Old 03-02-2012, 07:06 PM   #11
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Banging return line


Reduced temps to 150 and 170 as you suggested.
5 on/off cycles and all is quiet, Thanks!

Now I can wait till the weather warm up a bit to replace the suspect air valve on top of the expansion tank.
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Old 03-03-2012, 10:56 AM   #12
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Banging return line


Well , the baning started again about 2am when the heat came on.
Same noise from the Expansion Tank/Air vent and same dancing pressure indicator.
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Old 03-03-2012, 12:49 PM   #13
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Banging return line


Are you sure the plumber just didn't introduce a lot of air into the system when he did the repair and the noise you now hear is the air purger on top of the fill-trol tank removing the air. I am assuming you have a fill-troll tank with an air purger mounted on top with a air vent on top of that. Some pictures would help here. As long as my assumptions are correct I would push down on the pin in the air vent valve on top of the air purger a little and see if you are getting any air out. Don't activate the air valve that goes directly into the tank. This is at the bottom unless they mounted the tank upside down. This valve is for pre-charging the tank with air before it is put into use. key word here is "pre-charge". There is nothing to check here with a tire guage in an operating system. It will read same as the system pressure guage. You may want to go to the amtrol site and do some reading.
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Old 03-03-2012, 01:27 PM   #14
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Banging return line


And since the exp tank does seem OK with 1/2 sounding hollow and one half sounding solid, check if there is a shut off between the tank and the air purger, thats in the off position. Plumbers are now more commonly installing those valves for easier tank change outs.

Pictures would help!
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Old 03-03-2012, 02:03 PM   #15
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Banging return line


Thanks Guys.
Yes it's the Fill-trol with with an autmaic air vent on top. There is no way to manually release air, and the valve as some dried up crud under the plastic cap so not sure it's working anymore.

I'll get some pics up when I get home tonight.

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