Ayuh,... Ok, in the 3rd picture, of the tank. 'n the cast iron box, 'n there's a green handled ball valve, that's open...
Where does it come from,..??
If it's line pressure, domestic water supply, the pressure is Way to high...
Shut the valve Off, 'n bleed the drain valve on the boiler to lower the pressure to 'bout 15 psi...
Donno how it coulda ever worked Right, that way...
Im assuming that what you mean by the Auto-Fill is that large rectangular body sitting directly above the expansion tank. If so that thing is plumbed on both ends into what looks like a one inch line on both ends. It is threaded onto the tube fittings, but the male threaded ends are sweated into place.
Nope, that's just an expansion chamber to knock air outa the system, 'n the auto-bleed is the brass lookin' thing on top...
Is the rust from leakin' threads, 'n just sputter from the auto-bleeder,..??
Attached by 1/2 inch pipe there is another much smaller rectangular valve that is threaded into the top of the expansion tank. Could that valve be at fault.
I doubt it...
Gotta get a handle on the feed water,...
Where's that ball valve in pic #3 line come from...
That's where the auto-fill valve set to 12 psi oughta be...