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Is this Expansion Tank in Attic Draining Water?

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Member Posts: 80
Hey so we installed a new hot water boiler and was trying to fill system but pressure would never get above 5psi. Water pressure is good and don't see any leaks.

• Member Posts: 9,843
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Where does that overflow line go? You wouldn't fill that system to a pressure, you would just fill it until that expansion tank is more or less full. In many systems that overflow line runs in to the basement so you can tell when water starts running out of the tank but it could go somewhere else too. That is why old pressure gauges were called altitude gauges and marked in feet of water so you could fill it until the pressure reached the height of the tank.
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Is that old expansion tank still connected to your heating system? Sometimes they were replaced with a tank in the boiler room when gravity systems were converted to forced circulation.

Bburd
• Member Posts: 1,388
edited August 2022
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Hello @Dairon421, If your system stays at 5 PSI.

5.0 (PSI) / 0.4335 (PSI, 1 Foot of Head) = 11.53 Feet.

I would start looking for the leak (or overflow pipe) at 11.53 Feet above the gauge, assuming the gauge is working correctly. And if that is the height of that horizontal pipe connected to the top of the tank in the picture I would find out where it goes (or drains to), just so you know.

What did the old Boiler gauge read or was it defective ?

National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System
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The elevation from the top of that tank down to your boiler gauge will determine the most pressure you will get from that system.

If the tank is full then that is usually all you need....once all the air is out of the piping/rads.

10' will give you about 5 PSI. 30' will give you about 14 PSI.

If you keep adding water the overflow water will go somewhere.
Perhaps out onto the roof or rain gutter.
Maybe connected in the attic to the sewer vent or dropping down a wall to the basement drain lines or laundry sink.

You have 2 pipes connected into the bottom....my best guess is that one is a connection to the supply piping and the other to the return piping.

This induces water circulation into the tank, just like a radiator, to keep it from freezing in the attic.

Is there a pump on the new boiler?
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Assuming that tank is still active -- and it sounds like it is -- 5 psi is all you'll get unless the house is very tall. But -- that's not a problem! That's all you need, so not to worry.

I would find out where that overflow line goes, though...
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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My bet is on the roof and down a gutter wee it may not be noticed
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I've seen many attic tank overflows in Cleveland punched into the main sanitary stack vent. Not kosher today but Ohio didn't even have a Plumbing code until 1922 so the guys just did whatever worked prior to that.
gwgillplumbingandheating.com
Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

• Member Posts: 2,307
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mattmia2 said:

Where does that overflow line go? You wouldn't fill that system to a pressure, you would just fill it until that expansion tank is more or less full. In many systems that overflow line runs in to the basement so you can tell when water starts running out of the tank but it could go somewhere else too. That is why old pressure gauges were called altitude gauges and marked in feet of water so you could fill it until the pressure reached the height of the tank.

Those were the good old days when stuff worked forever. Some suction on overflow got air out.
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I've seen many attic tank overflows in Cleveland punched into the main sanitary stack vent. Not kosher today but Ohio didn't even have a Plumbing code until 1922 so the guys just did whatever worked prior to that.

Can you imagine that?
Guys thinking and doing what works instead of just following rules and having no idea why.

I'm not saying we shouldn't have codes. It would just be nice if more people would use their brain more.
Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment