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Old 03-03-2012, 02:52 PM   #16
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Banging return line


I thought you might have an air vent at the top like this:
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Banging return line-tank.jpg  

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Old 03-03-2012, 05:37 PM   #17
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Banging return line


Pics here , hope they help.
Attached Images
File Type: bmp boiler1.bmp (99.9 KB, 50 views)
File Type: bmp boiler2.bmp (99.4 KB, 50 views)
File Type: bmp boiler3.bmp (99.4 KB, 48 views)
File Type: bmp boiler5.bmp (99.4 KB, 48 views)
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Old 03-03-2012, 06:08 PM   #18
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Banging return line


My PC froze trying to download pictures 3 & 4.
Picture 2 shows an auto air bleed that you can test for air by removing the black plastic cap and use a small screwdriver or nail to push down the nib inside. Do this when the pump is off.
You shouldn't have to push any harder than you would on a bicycle tire valve to bleed off air. Sometimes it will vent and not stop dribbeling. In those cases, try doing it a few more times to see if it will stop. If that doesn't work then try putting the cap back on. When the cap is fully screwed down, that air bleed valve valve will not work. If nothing comes out when the nib is pushed down, that air bleed is broken or you dont have enough water pressure.
If air comes out, keep the nib down till only water comes out. If only water comes out, you don't have any signs of excess air in that area of your boiler.
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Old 03-03-2012, 06:09 PM   #19
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Banging return line


In boiler2.bmp isn't that an air vent on top? If you unscrew the cap it should be just like a tire valve. Pushing it in when you are getting the banging should help release some air. As long as all your valves are open, I'm betting the noise you are getting is your system releasing air introduced during the repair.
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Old 03-03-2012, 06:30 PM   #20
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Banging return line


OK.. last two pictures came through but are too blurry to tell for sure but it looked like your water pressure was way too low. Could you confirm that PSI again?
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Old 03-03-2012, 06:30 PM   #21
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Banging return line


I also notice you have an oil burner with a tankless coil. Once you solve your banging pipe issue you may need to return your aquastat settings to where they were if you don't have enough domestic hot water.
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Old 03-03-2012, 06:59 PM   #22
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Banging return line


PSI is right between 15 and 20 (unit not running)
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Old 03-03-2012, 07:03 PM   #23
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Banging return line


Yes, it is an air vent on top but there is nothing under the plastic cap to release water/air (like a on a tire).
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Old 03-03-2012, 07:15 PM   #24
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Banging return line


If you look down the air bleed on the auto air bleed valve (you may need to clean it if it is filled with crud) you should see a plastic x shaped stem.
That is what you'd normally press in to test that bleed valve.

The PSI you list is normal. Does that PSI rise closer to 30 when the banging is occuring?
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Old 03-07-2012, 09:43 PM   #25
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Banging return line


I replaced the air vent on top of the expansion tank this morning, but still have the same problem. clanking noise, pipes shake, and pressure gauge dances.

Aquastat set at 180h, 160 lo, and 15 diff. Boiler reaches 205 - 210 f, pressure
is steady at just under 30 until noise starts. Pressure never goes anywhere near as high as 30.
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Old 03-07-2012, 10:16 PM   #26
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Banging return line


Correction, pressure is steady at just under 20 until......
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Old 03-08-2012, 01:03 AM   #27
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Banging return line


This kind of rise in temp and noise without a pressure spike is usually associated with something causing poor water flow. When the boiler is cool and then turned on, a plumber will feel the outlet and return pipe from the boiler to confirm that the water is circulating. The outlet should warm up pretty quickly but the inlet stays cool until that hot water leaving the boiler makes its way through that zone back to the boiler.
When you turn up the thermostat on a zone when the boiler is cool (been off for an hour) how long does it take the return line to get hot?
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Old 03-08-2012, 06:13 AM   #28
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I'm off tomorrow and will have time to check this. I assume I should check
each zone independently? Should I be concerned that the boiler temp rises
20 to 25f above the Hi setting on the Aquastat?

Thanks again
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Old 03-08-2012, 11:19 AM   #29
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Banging return line


That temp override is high but not unheard of after the pump has shut off. If it occurs while the boiler pump is operating then it could be a sign of a water circulation difficulty.
I say "could" because it depends on what you notice of the temp on the return line into the boiler. Both the aquastat and the guage may also be inaccurate.
Are you hearing air escape from the new auto air bleed valve?
When you press in the stem from the bleed valve is it air or water that vents?
Is any water venting from the drain line from the pressure relief valve?
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Old 03-08-2012, 02:49 PM   #30
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Banging return line


No sound of air escaping from the new vent. I tried it several times and only got water. A few drops from the pressure relief valve in the past few days.

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