.3 gpm on hydronic heating -- help

Just spent the morning at the site and guess what?

You were all correct!

First I bled the system (this time correctly -- or at least, more correctly). Shut in/out valves to manifol, connected garden hose and one by one purged the circuits with the little bleeder tube. Lots and lots and lots of air came out. Fired it back up and got 1gpm through each circuit. I thought: "I'm done. Those guys really know what their stuff"

Waited 10 minutes and the flow dropped back down, to .8, then .6, then back to .4.

Bled it again thinking I must not have gotten all the air out.

Same thing: Good, then bad again.

Put an amprobe on the circulator and it's drawing just under half an amp. I don't know what it's supposed to draw, but I figured .5 amps can't be too far off.

Put a pressure gauge on the secondary piping and raised it to 20psi. I should have done this before doing anything, because I'm sure my steps up to this point messed with the pressure a lot.

Same low flow.

I removed the Y strainer's strainer and sure enough, the thing was full of rust colored stuff and filled the metal mesh. Removed the strainer and the flow is great. I can get 1gpm through each of the 4 circuits, but I lowered it to .8 for now.

Watched it for a few and it seems fine.

But I wonder where all the rust came from? I am using a well, but I've got a 50 micron filter between the boiler's water feed and the well.

So now I have the system running without the Y strainer's strainer. Should I be worried? Should I replace the strainer?

Thank you all very much!