Conventional Expantion Tank Fills Up - Plumbing - DIY Home Improvement | DIYChatroom

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Old 11-09-2009, 06:22 AM   #1
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Conventional expantion tank fills up

I have a boiler with a single zone feeding cast iron radiators. Their is a large conventional expansion tank in the ceiling (I figure 25 gallons or so). To drain it I off the valve to the tank and let it drain. It takes about an hour to get all the water out with the vacuum lock but I am positive that it is empty because I can lift if up and feel it. As soon as I turn the valve back on and run the boiler a few hours she is full again. Am I using the wrong procedure to drain the tank?
Yes I know I can replace it with a diaphram tank. I'd rather get this one working properly.


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Old 11-09-2009, 07:43 AM   #2
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How do you know that it is full? Does the temperature/pressure relief valve on the system open to blow off excess pressure? An expansion tank will fill partially with water under normal conditions.


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Old 11-09-2009, 04:41 PM   #3
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Last edited by Marlin; 11-09-2009 at 05:18 PM.
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Old 11-09-2009, 04:44 PM   #4
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There might be a tiny leak near the top of the tank or in a valve at the top of the tank causing loss of the air inside.
The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.
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