Recharge diaphragm expansion tank for boiler without disconnecting?

mikehvac

Recently installed an amtrol extrol diaphragm expansion tank for my boiler since the previous one was water logged causing my relief valve to drip. Says it was pre-charged to 12 psi but my relief valve (also recently replaced) is still dripping. I have a 3 story house so I assume I should've increased to 17 psi. The pipe to the expansion tank has a ball valve so I can isolate it, but I don't see a drain on the expansion tank - do I need to remove it from the system in order to drain the water/pump air and increase the psi?

Jamie Hall

Yes. The tank must be empty of water to precharge it properly.

That said, do you have a pressure gauge on the system? And what does it say? Cold and hot?

JohnNY

If you think it's not ruptured, then you can try giving it a few pumps with a bicycle pump or whatever you've got while it's still connected. It's a guess but it may work. I've done it successfully plenty of times.

STEVEusaPA

Are you sure your pressure gauge is accurate?
Did you properly purge the system of all air.
Are you sure your feed valve isn't letting water by? Or your tankless coil or indirect (if you have one) doesn't have a leak-allowing street pressure to raise the boiler pressure?

mikehvac

No tankless coil or indirect. Pretty sure system is purged of all air, it wasn't previously and we had some radiators that didn't work but after re-purging, all radiators work properly. No pressure gauge on the system. The replacement expansion tank is brand new so shouldn't be ruptured.

The pressure of the tank shows 24 psi - I assume that's expected since the tank isn't currently empty of water, and that the empty tank equivalent would be 12 psi, in which case I can increase the psi by 5 to get to 29 psi filled/17 psi empty?

STEVEusaPA

No. You're just guessing at this point. Get a pressure gauge. Watts makes a 0-30 that screws on to a hose bib connection.
Tank pressure needs to be checked with 0 system pressure on it-unless you have a valve like this on it to isolate it:

Set the tank pressure, then refill/repurge until your system pressure gauge shows the same pressure.

mikehvac

Thanks. What are the symptoms of an expansion tank that is undercharged (ET psi < system pressure) - leaking at the relief valve? Similarly what are the symptoms of an expansion tank that is overchaged (ET psi > system pressure)?

STEVEusaPA

Undercharged, overcharged, system not properly purged, usually all end up at the same result-rising pressure, blows out the relief valve. Which is why you need a good gauge on your system.

Solid_Fuel_Man

If your air gauge shows 24 psi, then your system pressure is likely 24 psi as well. 

You need a pressure/temperature gause on the boiler. And a nice web stone isolation valve, or at least a boiler drain T'd in between your ball valve and the Ex tank. 

SuperTech

You should have changed the relief valve as well.  Usually when they start dripping, they don't stop. If everything else checks out with the expansion tank and boiler pressure I'm sure thats your problem 

Mr_Doyle

number 1 dont read pressure of the tank at all when system is filled. you need to drain all water pressure off boiler. then you can read the tank pressure. you have tons of variables. but no indirect or coil. if you replaced tank before and relief and its still doing it. its simple feed valve is bad. replace it. how do you get your hw? if the tank is old. and low at all on charge. its compromised. don't add air. it obviously went somewhere. oh and most systems are fine between 15 and 18lbs at full temp.

EBEBRATT-Ed

I agree with @Solid_Fuel_Man

If the tank was factory charged to 12 psi and you have 24psi your water feeder is likely the problem. 24 psi in the system will be close to making your relief valve drip when the water heats up.

Check the feeder. And install a drain between the expansion tank and the isolation tank, check the expansion tank pressure when you remove it. Adjust to the pressur e you need