I don't know I get the impression he's just opening up the heat exchanger wide-open and of course the temperature will drop rapidly you have to know how the baby heat exchangers on these smaller machines to get max heat performance
What I am understanding is that the machine is just sitting there with no pump on and generating heat and when he turns the pump on.. And the water starts moving.. Its going to be cooler because there is a difference between the water sitting and heating... And water moving and heating.. But that being said.. I would it think it would be a bit warmer than he is describing... So something may be obstructing the flow
Bimba / diverter systems= better temperature control, more complexity to system.
Manual damper control= less temperature control, simpler system. With a manual damper it is not unusual to see your solution temperature have very high spikes if not moving water through the system.