Re-pressurize system after changing expansion tank

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Old 09-13-16, 04:30 PM
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Re-pressurize system after changing expansion tank

Hello there,
I have a question about how to pressurize system when replacing expansion tank.
I have successfully taken the old tank off, and am about to go buy a new expansion tank(hopefully already pressurized to 12psi). The boiler is currently at 0 psi, but I'm sure theres still water in there as the old tank was full of water.

I'm not sure what order to install the new tank, do I install it, turn water on, bleed from the baseboards? I also read somewhere I should increase the 12psi to 15 before installing it.. I'm not sure what exactly the psi is for the boiler, the regulator says 12-15psi.

I'm also not sure if the regulator is working properly. I had a plumber come take a look and he said it "might" not be working aswell as the expansion tank.. and wanted $700 to replace both.. but I'm not sure how to test it without the expansion tank on. Can I simply turn the water in-let valve and see if it goes above 12 psi? Even without the expansion tank? If anyone knows anything about that, help is greatly appreciated!

Thanks a lot!
 
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Old 09-14-16, 06:54 AM
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If the expansion tank was not leaking water (i.e no water came out of the Schrader (air) valve), you probably do not have to replace it. You can pressurize it with a tire pump or compressor while it is not connected to the system. Then reinstall it and turn on the makeup water. If you did not drain the system to take it off then you will not have introduced air into the system and will probably not have to bleed the system.

Install a valve (like this: http://www.supplyhouse.com/Webstone-...-Drain-600-WOG between the tank and the system and in future you can check the expansion tank by closing the valve and draining the tank and add air pressure if needed.

For a two story or less house, 15 pounds should be sufficient.
 
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Old 09-14-16, 07:07 AM
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Sorry forgot to mention it's the diaphram type tank, based on what I read when those become water logged they must be replaced. I do have a shut off valve unfortunately I think there must be air in system as i heard air in the pipes last year.

Should I turn on the water and see what the psi gets to without the expansion tank to see if the regulator is working properly? Or should I just screw in the new expansion tank and open the inlet valve until it hits 15 psi then shut it off and make it a closed system?
 
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Old 09-14-16, 04:14 PM
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the diaphram type tank, based on what I read when those become water logged they must be replaced.
No, not correct.

Should I turn on the water and see what the psi gets to without the expansion tank to see if the regulator is working properly?
No.

What you should do is depressurize the system and then, and only then, check the pressure in the old tank. With a bike pump, pump it up to about 15 psi. Then, re-pressurize the system.

If you are bound and determined to replace the tank, check the pressure in the new one before it is installed - and add air if necessary. Install the new tank and re-pressurize the system.

I think you are getting some bad info somewhere.
 
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