We were called out for water on the floor near tankless. Water had dried up by the time we arrived, but it appears that condensate line had frozen and overflowed. We also found that the thermal expansion tank had failed. We installed a condensate pump, and upsized condensation drain to 1” in an attempt to cut down on the possibility of the condensate drain freezing. We also replaced thermal expansion tank and replaced a swing check valve with a more reliable spring check. We I stalled an ion 6 water conditioner, so the unit will only require being flushed once every 4 years. We flushed the unit as a courtesy while onsite.