I mentioned there were several things wrong with the first installation of boiler piping. When tested, water was not getting through the system and I believed the pump was just not strong enough to circulate through all the radiant loops. That would be solved by changing the simple single looped system to the more common and complex primary/secondary piping.
After pulling out the pipes and rerouting into the new configuration, there was still a problem with the water getting through the system. It turned out that the valves are configured to open only one way. At some point I was looking for the recommended pump location and got into my head that I could assume the valves flowed down. I did remember the valves should be on the cold side to limit wear and tear from the hot water. But it was not obvious to me which way the valves opened. I thought since the lever that holds them open manually was on the bottom of the valve, that the flow was from top to bottom. Incorrect assumption!
Of course I was not looking at this obvious diagram, but at this installation.
If you know what you are looking at in the above photo, you can see that the air scoop and expansion tank are on the lower pipe. Typically they are on the hot side, but NOT ALWAYS in older, existing installations. So I assumed (again) that the higher pipe was the hot supply.
The flow is shown in this photo and is obvious now that you know the valves flow upward.
The lower pipe is the hot supply with the water flowing directly into the radiant/registers. On return the Honeywell flow valves are controlled electrically based on thermostat temperatures. The return water can also bypass the valves to bleed the system of air.
The major error in the piping was that twice both in the simple loop and in the first attempt at primary/secondary, I plumbed the hot into the upper pipe. After some consideration, I realized the error and replumbed all the piping so that the lower pipe was the hot supply. This meant remounting the secondary pump and I had to buy more 1″ copper and more fittings to reconfigure everything. The pipes seem more complicated than they should be but I could not figure out how to clear up what is a typical rats nest created by an inexperienced plumber, but at least now the plumbing is correct and the water flows properly.