Help - Corrosion on expansion tank


Old 09-25-14, 03:02 PM
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Help - Corrosion on expansion tank

I recently noticed that there is some corrosion on the piece above the expansion tank. I don't know if it's called a float valve or pressure release or whatever. The top piece of this, which looked like it was a plastic screw at some point is broken off , so I can't unscrew it. It looks like this piece screws into the top of the expansion tank. I think I need to change it, but I don't know if I can just unscrew it and put a new one on, or if I first need to drain the pipes from the baseboard somehow. There is no shut off nearby, and I'm not sure how to drain the water. I attached some pictures if anyone could help. I think I have a few questions.

It looks like the pipe in the last picture just goes down to the floor and is open. Maybe that's where I can let the water out?

1) How do I shut off the boiler?
2) How/do I need to drain the pipes?
3) How do I change the pressure release valve?
4) Do I need to do any maintenance on the expansion tank?
5) How do I fill the pipes back up and make sure there is no air in them?
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Old 09-25-14, 03:25 PM
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The smaller top piece is (or was) an air eliminator. It is now hopelessly corroded due to leakage and lack of maintenance. The larger device, between the air eliminator and the expansion tank, is a an air separator. The air eliminator has to be removed and replaced. From your pictures, I can't tell what valving you have to isolate the air eliminator from the rest of the system. Check to see yourself. If you can't isolate it, you will have to depressurize the boiler and drain below the elevation of the air eliminator, through the boiler drain valve.

After and while the system is depressurized, check the air pressure in the tank with a tire pump. With a bike pump, inflate it to about 12-15 psi.
Old 09-25-14, 05:11 PM
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If you drop the pressure in the boiler to zero by shutting off the water supply and draining until the gauge says zero...

And you cover the top of the boiler so that water can't splash on the controls...

And you prepare the new vent for installation by having it close at hand...

YOU WILL NEED TO BE SURE TO HAVE THE CORRECT ONE ON HAND! They come with different thread sizes. They typically are 1/8" thread, but yours looks like it might be 1/4" thread.

Look closely at the air scoop and tell us the make and model. It should be cast into the iron.

You can remove the old one, quickly put a finger over the hole, grab the new one, remove the finger and QUICKLY thread it in, you won't have to drain more than a little bit of water.

While the pressure is down on the boiler, take Gil's advice and check/charge the expansion tank.

There are STEP BY STEP (do not deviate from the instruction or it still won't be right) instructions in the thread below for a method to PROPERLY charge the air side of an expansion tank.

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