Thank you!

nibs

Thanks to all here especially those who answered my questions and to @Alan (California Radiant) Forbes for telling us about the Rinnai E50 Combi. Still owe Alan a lunch when we visit his neck o the woods.
Returned from Mexico about 5 days ago, to find the unheated house cold but otherwise in good shape, the thin slab floor was good etc.
Spent some time in Mexico reading Rinnai training manuals and working out the settings we should try on the boiler. The main changes we made was to lower the Min T set from the default 100F down to 90F and to lower the ODR from 14F down to 0F slowed the heat rise rate to 1F /minute. Now the system that was blasting away at 122F and shutting down for 6 or 8 hours is now modulating beautifully, 40F outside right now with the supply water about 93F at the manifold with a delta T of about 12F It is kinda neat to watch the boiler modulate as the outside temps drop at night.
The house has a huge thermal mass, with interior concrete walls and very thick exterior walls, it took 3 days to come up to temp.
I feel it would have been a much more difficult install and set up without this site and your help.
Thank you.
Tony.

Adolfo2

Good luck. I suspect that especially w/your situation NO SETBACK ever will be the preferred mode of operation.

nibs

Yes, am working with balancing to keep the Bedroom a couple of degrees cooler than the rest of the house.