Steel expansion tank and ATF-12

dxj100

Hello,

I need to drain my boiler down to replace a fitting on a baseboard heater that is wet. I have a steel expansion tank with an ATF-12. I know I have to do something with it when I refill the boiler. I can remember exactly what though.

Do I open the small port on the bottom and fill until water comes out or is it you open it until air comes out.

jesmed1

When refilling the expansion tank, start with the small fitting on the bottom of the ATF open (but don't unscrew it entirely). Start filling the expansion tank with water. At first, you should get air venting from the ATF fitting.

When water begins to flow freely from the ATF fitting, close it snugly and continue filling until water stops flowing into the tank. Then check your boiler pressure gauge and make sure your water pressure is where you want it.

Be aware that those boiler gauges can be inaccurate. I have a separate 0-30 psi gauge that I screw onto the outlet of my expansion tank (I also have an ATF-12). I use that to verify my water pressure because it's more accurate than the boiler gauge.

Full operating instructions for the ATF are here:

https://www.xylem.com/siteassets/brand/bell-amp-gossett/resources/manual/s10300h.pdf

You may want to follow the post-pressurization venting instructions too to get rid of the air you introduced by draining and refilling.

dxj100

Thanks. That's what I was thinking but then I started second guessing.

leonz

You have a compression tank.