SanCo2 issues – GreenBuildingAdvisor

My house used to be primarily heated by a propane fired modcon boiler (hydronic fan coil).  Before the tax credits expired, I moved over to heat pumps, with the boiler as backup.

The boiler also provided DHW via an indirect tank, but since I was barely using the boiler anymore (and, again, before the tax credits expired), I replaced the indirect tank with a SanCo2 unit (83 gallon).  I could not be happier with the efficiency, especially since the compressor unit is in my short basement (which hovers around 50-60 degrees in the winter and 70-75 degrees in the summer).

However, I am having one slight issue.  Whenever we aren’t home for 4-5 days straight, which happens somewhat regularly, the showers we take when we get back are not very hot.  They are hot enough for me, but not for people who like the water super hot.  I assume this is because the unit doesn’t want to kick on the compressor until the tank temp drops below 110 or something like that, but it’s not ideal.

Does anyone have any suggestions for how to fix this?  I have considered hooking the old boiler back into the mix via a sidearm or plate exchanger, especially since we will often use aux heat when we are coming home from being away for a few days, but I’m apprehensive about combining something like that with something as finicky as a SanCo2 as I don’t want to accidentally destratify my tank.

Open to any and all suggestions.  Maybe I simply need to tweak settings on the SanCo2 unit?