Psi rating for radient floor heat panel test???

You don't need to Rob, you can SEE it with soap

I would up the test pressure if you cannot get any soap

HOW ABOUT THE CIRCULATING PUMP shaft seal? Some of those are a mechanical seal. If you are unaware, that is more akin to piston rings, they may not use neoprene seals. I'm not a "boiler man." They may need water present to seal / lubricate

It may also be possible you have a defective bladder tank. I'd pull it and plug it off if any doubt. Look for anything else in that vein........AKA something that is not a connection. AND THAT includes valve shafts!!!!

Here's the other thing....anything above ground, "you can fix." If you get it down to close to "tight", I'd just fill it and run it and go from there. Leaks will become evident. Also "I guess" you are using glycol in the system, AKA antifreeze?