Delta T Pro DHW Controller

I recently replaced my old controller with a Heliodyne Delta T Pro Ethernet version.  I have the Grundfos flow/temp sensor as well as a half dozen 10K sensors for other temps.

I'm getting an inconsistent reading on Energy.  Some days it seems to chart the KBTU's properly, other days it will show  only a couple of hours with the intervening hours showing zero.  Some days it will not show any hours other than zero.

I have the Grundfos flow/temp box checked and the pressure /temp box unchecked because I don't have that sensor.

Question? Do I need both sensors to get reliable reading's?

I know the system is working because my tank right now is full of 137 F water!