Insufficient flow in radiant system (air removed via purge cart) looking for reasons?

To clarify, and I understand the horse has been cured (almost beat to death), but for the benefit of other people reading this string, the mixing specifications you've quoted are for the valve being used in an anti-scald (ASSE-1017 for example) in a DHW system, and do not relate to closed loop temperature control. I think no less than 6 people suggested you look at the mixing valve, because it is the only thing common to all circulators.

This is not rocket science or brain surgery. It's much harder than that. Even though You Tube say's it's not...

Glad you got your situation resolved.

ME