Replace expansion tank help

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Reach4

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I watched part of your video. I don't know hydronic systems. Once you started following the pipes around, I did not know that stuff. BUt I can say that unless you recently drained any water, that tank is not bad. After you have let some air out a few times, you should probably add some back and set the air precharge to the right level in the right way.

If you drained all of the water recently before the video, how much was there? If just a bit, I would concentrate on troubleshooting other areas. If it was a fair amount (I cannot translate that to tablespoons), then you could still suspect the expansion tank. If you continue to get new water, then replace the expansion tank. Therm-X-Trol would be a top (premium) brand.
 

Jadnashua

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Turn the boiler off, if the water is hot in the loops, you might want to wait awhile for things to cool off as it can be messy removing an expansion tank, and you don't want to scald yourself. You should never get any water out of the air fill valve...if you did, the bladder is leaking - it may be slow, but that's all it takes. If the tank ever fills up with water it is bad. If the air leak is small, it may take awhile, and it may only leak when things cycle a bit, but you should never get water on the air side. Without the proper amount (pressure) of air in the tank, when the boiler comes on and the water expands, it will force the excess out of the relief valve to lower the pressure. When the boiler shuts off, things cool, and the water contracts, so without that flexible air cushion from the bladder in the expansion tank, it might then just try to add some water from the autofill valve.

Close any valves you can to help reduce/prevent water from draining from everywhere to include the autofill (if you have one). Unscrew the old tank, and on the new one, before you install it, pump it up to the normal BOILER water pressure, which is typically somewhere around 15psi, but you need to know that value (NOT the supply water pressure, which the heating loop should never see). Once you have the new one on (remember the pipe dope and/or tape), turn the water back on and open any valves, and purge air from your system, then turn the boiler back on.

If you're lucky, the relief valve will close and seal...if not, you should replace it.
 

sealander

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I replaced the expansion tank today. before the boiler stayed at around 12psi and when it was running the pressure rose to about 18psi, now it stays at around 17psi and rises to about 20 psi while running. Is that normal?

Thank you again for the helpful responses!
 

Dana

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Watched your video. The valve with the lever on top is the auto-fill valve, which puts more water into the system if the system pressure drops below it's (adjustable) pre-set value.

The expansion tanks is on the heating system side and should be pre-charged to the pressure you set the system, which is apparently about 12 psi. If you pre-charged it to the street pressure (59 psi, you said?) rather than jadnashua's recommended ~15 psi it can't function as an expansion tank. So...

1: turn the power off to the system

2: close all the isolating valves

3: bleed air from the expansion tank until it's pressure reads ~ 12 psi

4: bleed water from the system (or let it cool off) until it's pressure gauge also reads 12 psi

5: open all the isolation valves- listen as you open up the valve by the auto fill to hear if the auto-fill adds any more water. If it does, re-check the pressure guage, confirming it's still ~ 12psi, give or take.

6: turn the power back on and run the system, and observe the peak pressure.
 
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