air build up in boiler

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Old 12-12-16, 09:00 AM
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air build up in boiler

I have to repeatedly bleed air from system. What would be likely causes? No visible leaks.

thanks
 
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Old 12-12-16, 10:12 AM
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W,
How are your bleeding the boiler. Are you building up enough pressure when bleeding so fresh water, which brings air with it, doesn't feed back in when finished.

Pressure should be up to about 28PSI, not to reach 30, when bleeding. When done drain off excess pressure to get to about 18PSI for normal operation.

Hope this helps.
 
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Old 12-12-16, 10:46 AM
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pressures water flow

By "bleeding back in" do you mean water going into the system from the water make up valve?

I set the thermostat for the zone to fire up the boiler/circ pump, then open a bleed valve on the zone and close the return valve from the zone to the boiler.

Water flows from hose to a bucket. Large air bubble forced out.

I've opened the small Scrhader type valve on the air vent. nver have air or water comimg out. Perhaps is is plugged?

thanks
 
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Old 12-12-16, 11:11 AM
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Might it be that what you're calling "air" is actually "steam" (or gaseous water) indicating that something in your Boiler is causing the water to become overheated ?
 
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Old 12-12-16, 02:00 PM
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Yes, I mean water feeding back in from the feed valve and you will probably always have air bleeding it the way you are.

Do not bleed with boiler and pump running. With boiler off pressurize system to just under 30 psi. Shut off isolation valve on return line and with constant high pressure bleed zone until a stead stream of water comes out. Don't be afraid to let it run to make sure you bled the whole loop.

When bleeding is complete drain off excess pressure back to about 20 psi and turn on your system.
Your air vent cap should be left loose to operate properly. If it leaks it should be replaced.
 
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