Hi Randy. Copy all and thank you for your quick reply.
Wiring from RL6, via J7-1 confirmed good (I checked all three for good measure).
Given you'd suggested the heater itself was bad, I then checked from L2 (black) across each of the cores (with the connectors unplugged from the control board so we didn't have any reverse reads back through the relays). I would expect with heating elements would be very high resistance wires to generate the heat. My inexpensive meter gave satisfactory >10M Ohm readings across two of the three elements but a virtual short on the third @27.4 Ohms.
Looking in on the heater from the rear, it's the element connector located at the top of the arc on the heater itself.
Are these items end-user replaceable or do I have to get a whole new heater unit itself?
Your recommended next step(s)?
Thanks again for your quick and clear response!