New boiler on gravity system

There is an approximately 18° hysteresis. So with a 115° element + 18° = 133° for the bypass to close off 100%

With a 130° element it takes 148° degree return to shut the bypass.

In my system I have temperature sensors on the supply and return to the boiler return and supply pipes.
Spot-checking these, I rarely see the return temperature get up to 133F - which means that most of the time, the system is running with the valve only partially open. I must admit that initially this was a point of concern for me, however in practice it seems to work quite well. There has been no issue whatsoever in keeping the house warm.

—Eric

I wonder why manufacturers of cast iron boilers don't simply partner with a company like Caleffi to provide what in my opinion is the best solution, namely a thermostatic mixing valve, as part of a turnkey system. Throw in a Grundfoss circulator while you're at it. Instead they leave it up to installers to do things however they want to do. But that's just me wondering.

—Eric