You missed the point for the OP, and didnt fully comprehend what I posted.
Also you are incorrect, the RC98 units show only combi use, no closed system heating use only, so the job you did is not condoned by Rinnai, so you have no warranty.
It can't be used as heating only, and to skirt the boiler safety laws, CSA & ANZI, it must be in a combi app only, with a DHW fixture draw if used for heating.
But rinnai and others recommend AH unit apps only, radiant or other types can't evacuate the stagnant water enough in the larger mass heating systems, thus there are safety issues.
In the end tankless aren't tested to CSA 4.9 safety standards as a boiler, so they will never have heating application ASME so why use them?
Read the whole letter here as proof to understand:
Good luck, tankless are not boilers as you stated yourself