Need to bleed my boiler to stop knocking noise

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Old 01-29-11, 01:30 PM
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Need to bleed my boiler to stop knocking noise

Hi. I have a gas boiler and it has been fine for the last few years but this winter it started making a lot of knocking noises when the heat is running through the pipes. I do not think it is the baseboards making the noise. The pressure was low so I increased the pressure to about 22 psi and that helped a little, but the remaining noise is very loud knocking while running and I think I have air in the pipes that needs to be bled out.

Here is a picture of my system:
boiler | Flickr - Photo Sharing!

I am thinking I need to open one of my two zones with (D) and then open (C) until there is no air bubbles coming out, then try again with (F)? Someone please tell me the procedure I need to follow to properly bleed any air from my system.

Thank you!
 
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Old 01-29-11, 01:55 PM
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When the boiler is cool, the pressure should be about 12 psi.

If you have that much air in your system, while the water is cool (100F or less), you can power purge each zone. Make sure the zone valves are closed. Connect a hose to (E) and run it somewhere for water to drain. Open the valve on (E) and then open the fast fill on the auto fill valve to force the air out of the zone. Repeat for (F).

You never want to put cold water into a hot boiler. There is a possibility that it can cause damage.
 
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Old 01-31-11, 06:50 PM
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Thank you so much! I did as you suggested and now no more noise. The fast fill would not fill nearly as fast as the valve would drain the water so I would let some out, build up pressure, let more out, etc; it took a while. But thank you once again for your assistance.
 
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Old 01-31-11, 08:12 PM
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My question is why was the pressure low? Will it happen again?
 
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