Remember the 9kw heater is a 2 Man unit.
It’s designed to be able to provide 2 users, very hot water.
One user is always going to get very hot water from it no matter the weather. (If it’s set up correctly)
I have to run mine on minimum setting in the winter, and then in summer I can adjust it higher,
Or I can adjust it higher for a Pvc clean etc.
I use the grippa hot water hose to, but I fancy trying my normal Hi vis hose. I find the red hose quite hard to manage.