My heater was always cold. I complained and the installed a 190 thermostat and moved the supply and return ports on the engine to improve performance. As I understand it, they've changed production to the 190 tstat. If you have the kit installed, just make sure that they don't cap the old supply port with a rubber cap (it splits and causes a lot of bad things to happen). The kit is supposed to come with a metal cap now, but they missed mine. Also, make sure they update software to raise the overheat alarm set point. I have to bring mine back in because it occasionally gives me overheat false overheat alarms now.
I didn't get the shower, so I can't help out your issues there.