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I keep on hearing a rattling sound like metal banging from 1 section of pipe in my hydronic heating system, I tried bleeding but no improvement. Thanks

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  • What kind of system? What age? What kind of water supplied to it for refill? Are there check valves in the system, how many zones? Can you isolate? Bleeding is primarily the common cause. Bleeding can be an art. If its confirmed not to be air, it might be worthwhile to flush (debris) and try isolating zones to make sure its not a negative flow issue. Are there any suspected leaks? Radiators or copper piping? – noybman Oct 31 '17 at 3:54
  • It's a regular hydronic system heated by a Slant Fin gas boiler with 4 zones but only 1 section of a few inches in 1 zone is noisy. Water supplied by city city water thru a pressure regulator and no valves only 1 at supply and 1 at return, and I isolated it while bleeding. – aofkj Oct 31 '17 at 6:34
  • Copper pipe to radiators. Was still noisy after closing all other zones. And no leaks. – aofkj Oct 31 '17 at 6:45
  • Is the system heating well? The impeller could be coming loose or the pump bearings worn. A zone valve could have a loose seat or paddle. When you bleed the radiation do you get water from all bleed valves you open or do you get some air then nothing? Do not isolate when bleeding. – d.george Oct 31 '17 at 10:16
  • Heating well, the noise isn't near any pump or valve and there are no bleeding valves on the radiators, I bleed thru a drain valve on each zone. I'm getting water the whole time. – aofkj Oct 31 '17 at 12:00
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A lot of radiators on hot water heat systems, if not, should have what is called a coin vent. These are located at the high points of each radiator. If you do not have these, you need to have them installed. Otherwise you will not remove all the air in the lines and will always have noise in your piping and it will cut down on the efficiency of the unit.

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