Thanks for the advice, Sean.

My unit is plumbed in the main line after the filter but before the booster pump (no heater or other stuff ). The flow switch is on the output side of the cell.

I didn't think I really needed to check the cell, even though that light was flashing, since it had only been running for less than an hour and was new (saw the packaging on that part) but will try that this AM.

For what it's worth, after I turned the unit off last night around 7, the display still read "Hot" after 11PM. I didn't want to worry about that all night, so I turned off the breaker to the unit.

I'll turn it back on this AM, check the cell and see what I can discover.

Thanks.